FIELD OF THE INVENTION

[0001] The present invention relates to natural gas distribution, and more particularly to a mobile letdown station for regulating a pressure and a temperature of a natural gas supply.

BACKGROUND OF THE INVENTION

[0002] Natural gas fuel is transported over long distances in large diameter transmission pipelines under high gauge pressures (e.g., about 250 to 1200 psi, or about 1720 to 8290 kPa) from natural gas processing facilities to local, permanently installed, pressure reduction stations (commonly referred to as a "regulation stations"). The regulation station reduces the natural gas gauge pressure (e.g., to about 60 psi, or about 400 kPa), before the natural gas is further transported in distribution pipelines to end use locations such as residential buildings. At or near the end use location, a permanently installed regulating device may further reduce the natural gas gauge pressure (e.g., to about 0.25 to 0.5 psi, or about 1.7 to 3.4 kPa) before the natural gas is supplied to appliances such as a heating furnace.

[0003] A regulation station may not be always available when needed. For example, the regulation station might be inoperable due to mechanical failure or an emergency incident. Also, a regulation station may not be available to service areas where utility infrastructure is undeveloped. Accordingly, it is known to provide mobile regulation stations (also known as "mobile letdown stations") in the form of a towable trailer with onboard pressure and temperature regulating equipment. Mobile letdown stations can be used to regulate natural gas supplied from a utility line, or compressed natural gas (CNG) that is stored onboard trailers and made available through networks of CNG compression stations in a so-called "CNG virtual pipeline".

[0004] Reliable operation of mobile letdown station is important for secure natural gas supply, especially in an emergency. Prior art mobile letdown stations require an electrical generator to power the onboard equipment such as programmable logic controllers (PLCs) that control electro-mechanical solenoid valves for pressure regulation, and heaters for temperature regulation. However, electrical power sources may not be available or reliable, particularly in an emergency. Further, electrical power consumption decreases the overall energy efficiency of the mobile letdown station.

[0005] Human operators may need to monitor and service the pressure and temperature regulating equipment onboard the mobile letdown station. At the same time, this equipment needs to be configured in compact manner. Often, this results in the equipment being laid out in a manner that is unintuitive to understand, and difficult or hazardous for a human operator to access.

[0006] Accordingly, there remains a need in the art for improvements in the reliability, safety, efficiency, and convenience of mobile letdown stations.

SUMMARY OF THE INVENTION

[0007] In one aspect, the present invention comprises a mobile letdown station for regulating a supply of natural gas. The mobile letdown station includes a wheeled trailer, and a regulating system onboard the trailer. The regulating system is for regulating the pressure or the temperature, or both the pressure and the temperature, of the natural gas between at least one inlet and at least one outlet of the regulating system.

[0008] In one embodiment, the regulating system includes at least one flow path that includes a pilot operated pressure regulator. In one embodiment, the regulating system also includes a heat exchanger, an electronic thermostatic controller, and a thermopile. The pilot operated pressure regulator is for decreasing pressure of the natural gas between the at least one inlet and the at least one outlet of the regulating system. The heat exchanger is for transferring heat from a heater to the natural gas between the at least one inlet and the at least one outlet of the regulating system. The electronic thermostatic controller is for controlling the heat output of the heater. The thermopile is for converting heat from the heater to electrical power for the electronic thermostatic controller. Accordingly, the pressure regulator and the electronic thermostatic controller are operable without any external electrical power, such as an ancillary electrical generator or electrical utility supply.

[0009] In one embodiment, the regulating system includes at least one pressure reduction stage. Each pressure reduction stage includes a pair of parallel flow paths. Each flow path comprises a pressure regulator for decreasing pressure of the natural gas between the a least one inlet and the at least one outlet of the regulating system. This arrangement allows for continued supply of natural gas even if one of the pressure regulators is rendered inoperable.

[0010] In one embodiment, each of the flow paths further comprises a pair of valves, wherein the pressure regulator is disposed in the flow path between the pair of valves for isolating the pressure regulator from the at least one inlet and the at least one outlet.

[0011] In one embodiment, each pressure reduction stage further comprises a bypass path that is parallel to the flow paths comprising the pressure regulators. The bypass path may comprise a manually operable valve for controlling pressure of the natural gas between the at least one inlet and the at least one outlet of the regulating system. This arrangement allows for continued supply of natural gas even if both of the pressure regulators are rendered inoperable.

[0012] In one embodiment, the at least one inlet comprises a plurality of inlets. The regulating system comprises a plurality of parallel inlet flow paths, each of which comprises one of the inlets and a valve for controlling flow of the natural gas from the one of the inlets to the at least one pressure reduction stage.

[0013] In one embodiment, the at least one outlet comprises a plurality of outlets. The regulating system may comprise a plurality of parallel outlet flow paths, each of which comprises one of the plurality of outlets and a valve for controlling flow of the natural gas from the at least one pressure reduction stage to the one of the outlets.

[0014] In one embodiment, the trailer includes an enclosed compartment defined by a floor, a ceiling, and vertical walls extending between the floor and the ceiling. The regulating system includes pressure regulating equipment disposed in the compartment. The pressure regulating equipment includes a flow path comprising a pressure regulator for decreasing pressure of the natural gas between at least one inlet and at least one outlet of the regulating system. The flow path is disposed along a periphery of the floor such that a central portion of the floor is unoccupied by the flow path. The area of the unoccupied central portion of the floor and the height between the floor and the ceiling may be sized to accommodate at least one standing human operator, and possibly more than one standing human operators.

[0015] In one embodiment, the at least one inlet is disposed external to the compartment, and one of the vertical walls defines an aperture for a conduit connecting the at least one flow path disposed within the compartment to the at least one inlet.

[0016] In one embodiment, the at least one outlet is disposed external to the compartment, and one of the vertical walls defines an aperture for a conduit connecting the at least one flow path disposed within the compartment to the at least one outlet.

[0017] In one embodiment, the regulating system further comprises a heater for heating the natural gas. One of the vertical walls may comprise a bulkhead wall separating the at least one flow path comprising the pilot operated pressure regulator from the heater disposed external to the compartment.

[0018] In comparison with mobile letdown stations in the prior art, embodiments of the mobile letdown station of the present invention as described herein may have features that make the station advantageous in the following respects. First, embodiments of the station do not require an external electrical power source for operation of the regulating system, thus avoiding the need for an ancillary electrical generator or electrical utility supply. Second, embodiments of the station may have redundancies in the pressure regulating equipment that allows for continued supply of pressure regulated natural gas even when part of the equipment is rendered inoperable. Third, embodiments of the station have pressure regulating equipment that is designed for ease of access, operation, training and servicing. Fourth, the embodiments of the station allow for relatively quick set-up and take down (e.g., less than 1 hours rather than up to 6 hours with prior art stations), thereby allowing the station to be rapidly deployed for use. Fifth, embodiments of the station have temperature regulating equipment that rapidly generate heat (e.g., within 15 minutes rather than 3 hours of start-up), thereby allowing the station to be rapidly supply natural gas after setup in low temperature environments. Sixth, embodiments of the station have a trailer that is relatively low in weight, increasing the ease with which the trailer may be transported. Seventh, embodiments of the station have a trailer equipped with an air suspension system which helps to protect the onboard regulating system. Eighth, embodiments of the station are equipped remote monitoring capabilities. Ninth, embodiments of the station allow for various high pressure inlet inputs (e.g., 250 psig to 3600 psig or more) and various outlet distribution pressure outputs (e.g., 400 psi or 15 psig to 100 psig). To meet distribution requirements, the distribution pressures (e.g., 15 to 100 psi) are protected by a pilot operated pressure relief valve that is not found on prior art stations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the drawings shown in the specification, like elements may be assigned like reference numerals. The drawings are not necessarily to scale, with the emphasis instead placed upon the principles of the present invention. Additionally, each of the embodiments depicted are but one of a number of possible arrangements utilizing the fundamental concepts of the present invention.

[0020] Figure 1 shows a front right perspective view of an embodiment of a mobile letdown station of the present invention.

[0021] Figure 2 shows a front left perspective view of the station of Figure 1.

[0022] Figure 3 shows a rear view of the station of Figure 1.

[0023] Figure 4 shows a side view of the trailer of the station of Figure 1.

[0024] Figure 5 shows a top floor plan view of the trailer of the station of Figure 1.

[0025] Figure 6 shows a rear view of the trailer of the station of Figure 1.

[0026] Figure 7 shows a rear view of the rear compartment of the trailer of the station of Figure 1, with pressure regulating equipment disposed along a periphery of the floor of the rear compartment. [0027] Figure 8 shows a side view of an embodiment of a line heater of the station of Figure 1.

[0028] Figures 9A to 9D, collectively, show a schematic process and instrumentation diagram (PID) of an embodiment of a regulating system of the station of Figure 1.

[0029] Figure 9A shows a first part of the PID.

[0030] Figure 9B shows a second part of the PID, continuing from Figure 9A.

[0031] Figure 9C shows a third part of the PID, continuing from Figure 9B.

[0032] Figure 9D shows a fourth part of the PID, continuing from Figure 9C.

[0033] Figure 9E shows a table of equipment identifiers for the PID of Figures 9A to 9D.

[0034] Figure 9F shows a table of valve identifiers for the PID of Figures 9A to 9D.

[0035] Figure 9G shows equipment symbols for the PID of Figures 9A to 9D.

[0036] Figure 9H shows a table of instrument symbol nomenclature for the PID of Figures 9 A to 9D.

[0037] Figure 91 shows a table of instrument signal lines for the PID of Figures 9A to 9D.

[0038] Figure 9J shows a table of instrument or function symbols for the PID of Figures 9 A to 9D.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0039] Definitions. Any term or expression not expressly defined herein shall have its commonly accepted definition understood by a person skilled in the art. [0040] Mobile Letdown Station. Figures 1 to 3 show one embodiment of a mobile letdown station (10) of the present invention. In general, the station (10) includes a wheeled trailer (12) and temperature and pressure regulating equipment collectively forming a regulating system onboard the trailer (12). These and other components of the station (10), and their use and operation are described in further detail below. [0041] Trailer. A purpose of the trailer (12) is to carry the pressure and temperature regulating equipment, and allow it to be transported to a desired location by a towing vehicle.

[0042] Figures 1 to 6 show one embodiment of a trailer (12) suitable for the station (10) of the present invention. In Figures 4 and 5, all dimension shown are in inches, unless specified as being in feet ('). The trailer (12) has a cargo area with a total length of about 22 feet (6.7 meters), and a total width of about 8 feet (2.4 meters). The trailer (12) is constructed from high strength aluminum for weight control, corrosion resistance, and vibration absorption. The total weight of the station (10) (i.e., the trailer (12) inclusive of the onboard regulating system) is about 10000 pounds (4500 kilograms). Accordingly, this embodiment of the station (10) has a weight that is within the towing capacity of many passenger pick-up trucks available on the market, and does not need to be towed by a specialized vehicle. In other embodiments, the trailer (12) may have different dimensions and weights.

[0043] In one embodiment, the trailer (12) may be equipped with an air suspension system to isolate the onboard equipment from shocks and vibrations during transportation, and to extend the useful life of the trailer (12). As known to persons of ordinary skill in the art of vehicle design, a typical air suspension system may include a pump or compressor powered by a battery or the vehicle engine to control the pressure in air springs, and thus vary the stiffness of the suspension and/or the ride height of the suspended components. In other embodiments, the trailer (12) may have other types of suspension systems.

[0044] In the embodiment shown in Figures 1 to 6, the trailer (12) has three discrete sections along its length: a rear section (14); an intermediate section (16); and a front section (18). These discrete sections allow the relatively hazardous and non-hazardous equipment to be isolated from each other. This in turn may allow for cost savings since the portions of the trailer (12) that support non-hazardous equipment may be constructed to less stringent safety requirements (e.g., fire rating) than those that support hazardous equipment.

[0045] In the embodiment shown in Figures 1 to 6, the rear section (14) defines a rear compartment (20) (see Figure 5) that houses the pressure regulating equipment of the regulating system, so as to protect such equipment them from the environment, dirt, and corrosive road salt. In this embodiment, the rear compartment (20) is defined by, and fully enclosed by a floor, a ceiling, and four vertical walls. The four walls include a pair of side walls substantially parallel to the longitudinal (front-to-back) axis of the trailer, and a front wall and a rear wall, both of which are substantially perpendicular to the longitudinal axis of the trailer. The floor of the rear compartment (20) has a rectangular shape with a length of about 8 feet (2.4 meters) and a width of about 8 feet (2.4 meters), and is preferably clad in a slip-resistant finish such as patterned tread plate. The ceiling is disposed about 11 feet (3.4 meters) above the floor. As shown in Figure 7, the pressure regulating equipment is disposed along the periphery of the floor of the compartment so as to leave an unoccupied central portion of the floor. The unoccupied volume of the rear compartment (20) is sufficient to accommodate at least one, and preferably several, typical adult human operators standing upright within the rear compartment (20) (e.g., the unoccupied central portion of the floor may have a width and a length of at least about 3 feet or 0.91 m by about 3 feet or 0.91 m, and the height between the floor and the ceiling may be at least about 6 feet or about 1.82 meters), and provides a shelter that protects the operators from the external environment. As shown in Figures 1 to 4, the side walls may have windows to allow light into the rear compartment (20). The front wall (25) may be constructed as a bulkhead partition to provide passive fire protection for the equipment in the rear compartment (20), and to protect the line heaters (36a, 36b) (as described below) in the intermediate section (16) in the event of a pressure-induced failure of the equipment in the rear compartment (20), while defining apertures for flow paths from the pressure regulating equipment to line heaters (36a, 36b). As shown in Figures 3 and 5, the rearmost wall (21) is inset from the rear end of the trailer (12) by about 1 foot (0.3 meters). As shown in Figure 3, the rearmost wall (21) has a lockable door (22) for through passage of a human operator into the rear compartment (20). Further, the rearmost wall (21) also defines apertures with fixtures that allows for inlets (24a, 24b) and for three outlets (26a, 26b, 26c) of the regulating system to be connected to a natural gas inlet line (28) and a natural gas outlet line (30), respectively, without exposing the equipment in the rear compartment (20) and without having to open the door (22). It will be understood that conduits passing through the apertures of the rearmost wall (21) allow for communication of natural gas between the inlets (24a, 24b) and the outlets (26a, 26b, 26c) outside of the rear compartment (20), and the pressure regulating equipment inside the rear compartment (20). As shown in Figures 3 and 6, the rear of the trailer (12) has a pair of lockable swing-out doors (32a, 32b) that allow for access to the external side of the rearmost wall (21), and provides further security for the equipment stored in the rear compartment (20). The rear of the trailer (12) also has a ramp (34) to provide ease of access to the rear compartment (20). In this embodiment, the ramp has a length of about 4 feet (1.2 meters), and a width that extends the full width of the trailer (12). The ramp (34) is bottom mounted to the trailer (12) with a hinge so as to be pivotable from a substantially vertical orientation for transport (see Figures 4 and 6) to an inclined orientation from the ground level to the floor of the rear compartment (20) (see Figures 3 and 4), which is about 1.38 feet (0.40 meters) above the ground level. As shown in Figure 6, when the ramp (34) is in the transport configuration, the ramp (34) overlaps the inlets (24a, 24b) and the outlets (26a, 26b, 26c), which may help to protect them during transport and to protect them from tampering. As shown in Figure 3, when the ramp (34) is in the deployed configuration, the ramp (34) may also be used to cover at least part of the inlet line (28) and the outlet line (30), thereby decreasing the tripping hazard that would otherwise be presented by such lines, and reducing foot traffic and resulting wear-and-tear on such lines.

[0046] In this embodiment, as shown in Figures 1 and 2, the intermediate section (16) is used to support the pair of line heaters (36a, 36b) of the regulating system. The floor of the intermediate section (16) has a rectangular shape with a length of about 12 feet (3.7 meters) and a width of about 8 feet (2.4 meters), and is preferably clad in a slip-resistant finish such as patterned tread plate. The intermediate section (16) is open to the surrounding environment, by virtue of an opening in the sidewalls and the roof of the intermediate section (see Figures 1 and 2), and separated from the rear compartment (20) by the front wall (25) of the rear compartment (20).

[0047] In this embodiment, the front section (18) defines a front compartment (27) that may be used to house additional non-hazardous equipment associated with the station (10), such as a battery that is charged by solar panels, and equipment associated with remote monitoring functions of the regulating system, as described below. By positioning the front compartment (27) more than 10 feet away from the closest high-pressure flange, the front compartment (27) is outside the Class 1 Division 2 hazardous location zone under the Canadian Electrical Code ®. Accordingly, the equipment stored in the front compartment (27) does not need to be classified for a hazardous area. As a result, this increases the range of equipment that can be used and decreases overall costs. In this embodiment, the floor of the front section (18) has a substantially triangular shape with a length of about 6.2 feet (1.9 meters) and a maximum width of about 8 feet (2.4 meters). As shown in Figures 1 and 4, the front section (18) may have a lockable door (38) for access by a human operator to the front compartment (27).

[0048] Pressure regulating equipment. A purpose of the pressure regulating equipment of the regulating system is to decrease the pressure of natural gas between an inlet line (28) and an outlet line (30) to a desired pressure. In one embodiment, as anon-limiting example, the pressure regulating equipment may be configured to down regulate the gauge pressure of the natural gas to about 250 psi from about 3600 psi (to about 1720 kPa from about 24800 kPa) from the inlets (24a, 24b) to the outlets (26a, 26b, 26c). In another non-limiting example, the inlet gauge pressure may be reduced from about 4700 psig or about 32400 kPa. It will be understood that the present invention is not limited by any particular inlet pressure or outlet pressure.

[0049] In one embodiment, as shown in Figure 7, the pressure regulating equipment is contained in the rear compartment (20) of the trailer (12). More particularly, the pressure regulating equipment is installed along the periphery of the floor of the rear compartment (20), in close proximity to the walls (e.g., within about 3 inches of the walls) so that vast majority (e.g., over about 50 percent, and preferably more than 75 percent) of the total area of the floor in the center of the rear compartment (20) remains unoccupied to accommodate a human operator. Moreover, components of the pressure regulating equipment are preferably installed in a single "layer" on the walls so as to avoid components overlapping each other. This allows a human operator to readily view, understand and access individual components of the pressure regulating equipment when standing inside the rear compartment (20), which in turn facilitates operation and servicing of the individual components, with lower risk of operator error.

[0050] In one embodiment, the pressure regulating equipment comprises one or more pressure regulators to decrease the natural gas pressure between the inlets (24a, 24b) connected to an inlet line (28) and the outlets (26a, 26b, 26c) connected to an outlet line (30). As used herein, "pressure regulator" refers to a valve with a body, and a movable flow restricting element that varies the restriction to fluid flow through the body so as to selectively reduce the pressure of the fluid from the inlet to the outlet of the body. A pressure regulator may be one of many types known in the art such as a globe valve, a butterfly valve, or a poppet valve. Preferably, the pressure regulator is selected to be operable under a range of operator pressure and temperature conditions, and readily serviceable.

[0051] In one embodiment, the one or more pressure regulators are pilot operated. As used herein, "pilot operated" means that the moveable flow restricting element of the pressure regulator is actuated by fluid pressure in the system acting on different areas of the flow restricting element, without the need for an electrical power source. Accordingly, pilot operated pressure regulators may reduce or avoid the need for an electrical power supply at the station (10). Non-limiting examples of suitable pilot operated pressure regulators are available under the tradename Swagelok™ (Swagelok Inc., Solon, Ohio, United States). Conventional pilot operated pressure regulators are known in the art and are therefore not illustrated herein in detail, but are shown symbolically as pilot operated pressure regulators (44a to 44f) in the PID of Figures 9B to 9D.

[0052] Temperature regulating equipment. The natural gas supplied by an inlet line (28) to the inlets (24a, 24b) of the station (10) may be below a desired temperature for use by an end user due to the natural gas being provided in a cold temperature environment. Moreover, natural gas passing through the pressure regulator(s) will decrease in temperature as a result of the Joule-Thomson effect. In the absence of externally applied heat, the temperature decrease may allow for undesirable formation of hydrates in the outlet line that impede the flow of natural gas in the outlet line.

[0053] Accordingly, a purpose of the temperature regulating equipment is to heat the natural gas between the inlet line (28) and the outlet line (30) to a desired temperature, which is preferably above the temperature at which hydrates may form in the outlet line (30). The temperature regulating equipment includes at least one heat exchanger for exchanging heat produced by a combusted fuel to the natural gas.

[0054] In one embodiment, as shown in Figure 1 and 2, the station (10) comprises two heat exchangers that are installed in the intermediate section (16) of the trailer (12). In one embodiment, as shown in Figure 8, each of the heat exchangers comprises a heater in the form of a line heater (36) that operates in accordance with principles described in Canadian patent 2,511,034 C, the entire contents of which are incorporated herein as if reproduced herein, where such incorporation is permitted. It will be understood that the "tube side" of the heat exchanger connects with the flow path of the pressure regulating equipment in the rear compartment by an inlet flange (40) and an outlet flange (42). Each line heater is what is known as a heat driven loop. It operates under a vacuum, and as a result, a much smaller volume of glycol is required than in a typical line heater. The coil or tube containing the gas to be heated is suspended above the glycol in a vacuum. Finned heat exchanging tubes transfer heat from a natural gas flame to the glycol which evaporates at a low temperature due to the vacuum. The glycol steam then condenses on the cooler gas coil transferring the heat through the coil wall to the gas. The condensed glycol then drops back down to the heat exchanging tubes where it is reheated in a continuous loop. The smaller volume of glycol in this style of line heater allows for reduced overall weight and fast warm up times and the vacuum increases the efficiency of the thermal transfer resulting in less gas being used for the heating process. Non-limiting examples of such line heaters (36) may be available from Tecvalco Ltd. (Niagara Falls, Ontario, Canada). Preferably, the line heater (36) is selected so as to be light in weight, efficient in heat transfer, and capable of warming up rapidly (e.g., in less than 15 minutes in cold temperature environments.) In other embodiments, heat exchangers and heaters that operate in accordance with other principles may be used in the station (10).

[0055] In one embodiment, the temperature regulating equipment also comprises a thermostatic controller to control the operation of the line heater (36) so that the natural gas is heated to a desired temperature. In one embodiment, the thermostatic controller may comprise an electronic thermostatic controller. Conventional electronic thermostatic controllers suitable for use with the present invention are known in the art are therefore not illustrated herein in detail, but are shown symbolically as electronic thermostatic controllers (48a, 48b, 48c) in the PID of Figures 9C and 9D. A non-limiting example of a suitable thermostatic controller uses temperature-sensing capillary tubes that are inserted in thermowells (50, 52) in the inlet tube and outlet tube of the line heater (36) (see Figure 8), such as the Honeywell model T675A™ temperature controller (Honeywell International; Morris Plains, New Jersey, USA). In other embodiments, the thermostatic controller may operate in accordance with different principles. The operation of electronic thermostats requires an electrical power source. Possible electrical power sources include an electrical utility line, or an electrochemical battery. However, electrical utility lines are not always been available, and batteries deplete with use. Accordingly, in a preferred embodiment, the thermostatic controller may be operatively connected to a thermopile. The thermopile, converts heat produced by the line heater (36), to an electrical current to power both the electronic thermostatic controller and an electrically powered valve that controls the supply of fuel gas to the line heater (36), and thereby controls the heat output of the line heater (36). As a non-limiting example, the thermopile may be heated by a pilot flame of the line heater (36). Conventional thermopiles are known in the art are therefore not illustrated herein in detail, but are shown symbolically as thermopiles (56a, 56b) as part of RTU flow computers associated with the line heaters (36a, 36b) in the PID of Figure 9B.

[0056] Regulating system. The pressure regulating equipment and temperature regulating equipment, as described above, collectively form a regulating system for regulating the pressure and temperature of the natural gas between an inlet line (28) and an outlet line (30) to a desired combination of pressure and temperature.

[0057] Figures 9A to 9D, collectively, show a schematic process and instrumentation diagram (PID) of one embodiment of a regulating system. In this diagram, the components are shown with identifiers or symbols that are conventional to persons of ordinary skill in the art, and further explained in Figures 9E to 9J.

[0058] In the embodiment shown in Figures 9A to 9D, the regulating system decreases the pressure of the natural gas in three pressure reduction stages or "cuts", arranged in series with each other. In the first pressure reduction stage as shown in Figure 9B, a first line heater (36a) (labelled E-l) pre-heats natural gas received from the inlet line (28) via inlets (24a, 24b) before it passes through a first pair of pilot operated pressure regulators (44a and 44b) (labelled PRV01 and PRV02) arranged in parallel flow paths. In the second pressure reduction stage, as shown in Figures 9B and 9C, a second line heater (36b) (labelled E-2) (see Figure 9B) pre-heats the natural gas before it passes through a second pair of pilot operated pressure regulators (44c and 44d) (labelled PRV03 and PRV04) (see Figure 9C) arranged in parallel flow paths. At this stage, if desired, the gas may flow to outlet (26c) and leave the trailer at 400 psig. In the third pressure reduction stage as shown in Figure 9D, the natural gas passes through a third pair of pilot relief valves (44e and 44f) (labelled PRV06 and PRV07) arranged in parallel flow paths before flowing to the outlet line (30) via outlets (26a, 26b, 26c).

[0059] Therefore, in this embodiment, the natural gas passes through a pair of pilot operated pressure regulators arranged parallel flow paths at each pressure reduction stage. This provides for redundancy in the regulating system. If one of the pilot operated pressure regulators (44a, 44c, 44e) of any of the pressure reduction stages is rendered inoperable, the continued operation of the other one of the pilot operated pressure regulators (44b, 44d, 44f) (or vice versa) in the parallel flow path of the same pressure reduction stage allows for continued supply of natural gas to the outlet line (30). Preferably, each of the pilot operated pressure regulators is sized so that it alone has sufficient flow capacity to meet the expected demand for natural gas at the outlet line (30). Preferably, each of the pilot operated pressure regulators (44a to 44f) is connected to the flow path with fittings that allow the pressure regulator (44a to 44f) to be removed from the flow path and replaced while the station (10) is operating. For example, as shown in Figure 3, the two pressure regulators (44c, 44d) of the second pressure reduction stage are vertically spaced apart from each other and connected to their respective flow paths with inverted U-shaped pipes and Swagelok™ fittings that allow each of the pressure regulators (44c, 44d) to be individually removed and replaced without interrupting the operation of the other pressure regulator (44c, 44d). In this regard, each of the pressure regulators (44a to 44f) is disposed in a flow path between two valves that allows for isolation of the portion of the flow path including a particular pressure regulator (44a to 44f) to be isolated from the inlets (24a, 24b) and the outlets (26a, 26b, 26c), without interrupting flow through the other pressure regulators (44a to 44f).

[0060] In the embodiment shown in Figures 9A to 9D, the equipment has additional features that allow for safe and convenient operation of the regulating system, as described below.

[0061] Hardline bypasses. As shown in Figures 9B to 9D, each pressure reduction stage includes a hardline bypass (46a; 46b; 46c) arranged in a flow path that is parallel to the flow paths containing the pressure regulators (44a to 44f). Each bypass (46a, 46b, 46c) has a ball valve that allows gas to be vented to the atmosphere, between two other ball valves. The upstream ball valve is sized to have the same flow rate (flow coefficient, CV) as the pressure regulators in parallel with it, so that if the hardline bypass is opened, the downstream relief valves can expel enough gas to prevent the downstream portion of the regulating system from being over pressured. The upstream ball valve of each bypass is locked when not in use to prevent accidental opening. The valves of the hardline bypasses allow for manual throttling of gas in the event of failure of both pressure regulators that are in parallel with it. Further, the ball valves can be opened if the inlet pressure is low to help bypass the restrictions of the pressure regulators.

[0062] Multiple inlets and outlets. As shown in Figure 9A, the regulating system has two inlets (24a, 24b) in parallel inlet flow paths so that the regulating system can be switched, using ball valves, from receiving natural gas from a first inlet line (28) (see Figure 3) to receiving natural gas from a second inlet line (not shown) without interruption of natural gas supply. As shown in Figures 3 and 9D, the regulating system has three outlets (26a, 26b, 26c). Outlets (26a, 26b) allow natural gas to be discharged after passing through the third pressure reduction stage. These outlets are in parallel outlet flow paths, each with ball valves, so that the regulating system can be switched to discharge natural gas to the output line (30) (see Figure 3) or another output line (not shown) . Outlet (26c) allows natural gas to be discharged after passing through the second pressure reduction stage (without also passing through the third pressure reduction stage), as discussed above.

[0063] Quick connect fittings. Preferably, all high-pressure gas connection points to the inlet line (28) and outlet line (30) use a high flow, quick connect fitting. Preferably, these fittings have safety features to prevent injuries: a locking collar; an indicator strip showing that connection is complete; and internal poppets that stop the gas flow if the inlet line (28) or outlet line (30) is accidently disconnected.

[0064] Needle valve to control initial inflow of gas. As shown in Figure 9A, a union bonnet needle valve (49) (labelled HV04) is provided to allow for controlled introduction of high-pressure gas from the inlet line (28) to the line heaters (36a, 36b) and pressure regulators (44a to 44f). This allows time for the pressure regulators (44a to 44f) to react, and for air to be purged from the regulating system. Once the regulating system is at operating pressure, a full port ball valve (51) (labelled HV05) bypasses the needle valve. [0065] Bleed valves. As shown in Figures 9A to 9D, numerous manually operated ball valves are provided to allow for venting of natural gas to the atmosphere, outside of the rear compartment (20) of the trailer (12). Collectively, these valves allow the regulating system to be depressurized before the inlet line (28) is disconnected from the regulating system, and before the regulating system is serviced or transported. Numerous pressure gauges are also provided to provide visual indicators to human operators of the presence of pressurized gas.

[0066] Pressure relief valves. As shown Figure 9B, a token pressure relief valve (53a) (labelled PSV01) is provided downstream of the first pressure reduction stage to alert operators to a problem with the pressure regulators in the first pressure reduction stage. As shown in Figure 9C, a pair of pressure relieve valves (53b, 53c) (labelled PSV02 and PSV03) are provided downstream of the second pressure reduction stage. By keeping all the tubing and the pressure regulators in the first and second pressure reduction stages the same, it is possible to use this pair of pressure relief valves after the second pressure reduction stage, as opposed to a pressure relief valve downstream of each of the first and second pressure reduction stages. As shown in Figure 9D, a pressure relief valve (53d) (labelled PSV04) is provided downstream of the third pressure reduction stage. The pressure relief valve (53d) is pilot operated so that the gas provided to the outlet of the regulating system can meet pressure requirements for feeding gas into a distribution regulating system. A pilot operated pressure relief valve tends to be more sensitive and accurate than direct-operated relief valves for overpressure protection, and may better comply with regulatory requirements pertaining to natural gas supply. This pressure relief valve (53d) may be an axial flow valve with a manifold to select between two pilot valve with different pressure ranges (e.g., a first range of about 3 to 30 psi (or about 21 to 210 kPa), and a second range of about 25 to 150 psi (or about 170 to 1000 kPa) so that an operator can select the desired relief pressure, without disassembly of the regulating system.

[0067] Drop legs. As shown in Figures 9A to 9D, the regulating system has multiple drop legs to catch and remove contaminants from the regulating system.

[0068] Full port valves. Preferably, all valves in the regulating system are full port valves (i.e., they have no restriction of flow in comparison to the pipes connected to them.) The use of full port valves helps to reduces gas turbulence and noise, and avoid the Joule- Thomson effect. Preferably, as shown in Figure 3, any manually operated valves are provided with large control handles to allow for greater precision of manual control.

[0069] Remote terminal units. As shown in Figures 9A to 9D, the regulating system includes microprocessor controlled electronic devices or remote terminal units (RTUs) (labelled PI01, PI012, PI03, TS01, and TS02) that are operatively connected to communicate with pressure or temperature sensors and provide information in human readable form regarding gas pressures at the inlet, and downstream of the second and third pressure reduction stages, and the gas temperature downstream of the second and third pressure reduction stages. These RTUs may be powered by batteries that are charged by solar panels attached to the trailer (12). The RTUs may also have communication modules that allow for transmission of date to computing devices that are located remotely from the station (10).

[0070] Use and operation. A non-limiting exemplary use of the embodiment of the station (10) shown in the figures is now described. The use of the station (10) may begin with a request to a human operator to deploy the station (10) to a site that requires gas service. The operator turns on the air suspension regulating system of the trailer (12) to raise the ride the height of the trailer (l2)'s chassis relative to its axles. A one-ton pickup truck may be used to tow the station (10) to the site. [0071] Once the station (10) arrives at the site, it needs to be setup for use. A high pressure natural gas source (e.g., up to about 3600 psi or about 24800 kPa) is connected to an inlet line (28) that is in turn connected to the inlet (24a, 24b) of the regulating system onboard the trailer (12). As non-limiting examples, the high pressure natural gas source may a compressed natural gas unit onboard another trailer, or infrastructure associated with an existing natural gas utility. Further, an outlet line (30) is connected to the outlet (26a, 26b, 26c) of the regulating system onboard the trailer (12), as well as to a customer receipt point. The regulating system onboard the trailer (12) is then purged of air, and filled with natural gas. The line heaters (36a, 36b) are then lit. The setup process is relatively straight forward, and may be completed within an hour. [0072] Once the station (10) has been setup, it is ready to be used. An operator opens the valves so that natural gas from the high pressure natural gas source flows into the regulating system onboard the trailer (12). The first line heater (36) preheats the gas, and the first pressure reduction stage decreases the gauge pressure of the gas to about 1400 psi (or about 9600 kPa). The second line heater (36) preheats the gas again, and the second pressure reduction stage further decreases the gauge pressure of the gas to about 400 psi (or about 2700 kPa). At this point, if high pressure gas is required, the gas can be discharged from the regulating system at about 400 psig via outlet (26c). The third pressure reduction stage further reduces the gauge pressure of the gas to an adjustably selectable pressure within the range of about 15 psi to 100 psi (or about 100 kPa to 690 kPa) at the outlet of the regulating system. The outlet line (30) supplies the gas to the customer receipt point for use by the customer.

[0073] Interpretation. References in the specification to "one embodiment", "an embodiment", etc., indicate that the embodiment described may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to affect or connect such module, aspect, feature, structure, or characteristic with other embodiments, whether or not explicitly described. In other words, any module, element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility, or it is specifically excluded.

[0074] It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as "solely," "only," and the like, in connection with the recitation of claim elements or use of a "negative" limitation. The terms "preferably," "preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

[0075] The singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise. The term "and/or" means any one of the items, any combination of the items, or all of the items with which this term is associated. The phrase "one or more" is readily understood by one of skill in the art, particularly when read in context of its usage.

[0076] The term "about" can refer to a variation of ± 5%, ± 10%, ± 20%, or ± 25% of the value specified. For example, "about 50" percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term "about" can include one or two integers greater than and/or less than a recited integer at each end of the range. Unless indicated otherwise herein, the term "about" is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

[0077] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. [0078] As will also be understood by one skilled in the art, all language such as "up to",

"at least", "greater than", "less than", "more than", "or more", and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges as discussed above. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.