Reducing pressure of compressed gas from tank

Abstract

A system that can unload compressed gas from a storage tank to a customer site. The system may have a fluid circuit configured to fit within a container structure, such as a trailer, for movement to a remote location. The fluid circuit may include a transfer unit for automatic switching between the tanks. The transfer unit may be coupled with the heat exchanger. Downstream of the heat exchanger, the fluid circuit may reduce the pressure of the fluid from the tank through a plurality of pressure reduction stages. Various pressure reduction stages may include throttling devices, such as pilot fluid regulators and control valve assemblies. The throttling device may be selected according to a pressure drop in the incoming fluid from the tank to maintain the fluid flow at at least, for example, 35,000 standard cubic feet per hour.

Description

This application is a divisional application of the PCT patent application "Reducing the Pressure of Compressed Gas from a Storage Tank" (national application number: 201680082705.X, applicant: General Electric Oil and Gas Company) which entered the Chinese national phase on August 27, 2018.

[0001] Cross-references to related patents This application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 62 / 271,237, filed on December 27, 2015, and entitled “REDUCING PRESSURE OF COMPRESSED GAS FROM A STORAGE TANK,” the contents of which are incorporated herein by reference in their entirety. Background Art

[0002] The delivery of hydrocarbons can utilize tanks that are transported by truck, ship, and rail. These tanks can carry large quantities of compressed gas at very high pressures. However, there is often a mismatch between the gas pressure during transportation and the pressure required by the customer to unload the compressed gas from the tank. Summary of the invention

[0003] The subject matter of the present disclosure generally relates to the unloading of compressed gases. Embodiments herein can distribute gas formed (found) at "high" pressure in a transport tank (e.g., a tube trailer) to a customer-specified reservoir. These reservoirs are often only configured to receive only gas at "low" pressure. As further noted below, some embodiments may incorporate components that can meet the pressure drop from the tank to the customer's reservoir. These components can keep the gas as a steam to avoid two-phase flow that can destroy the accurate and reliable measurement of the properties of the fluid distributed to the customer (e.g., temperature, pressure, flow, etc.). These components can also be automatically operated to allow multiple tanks to be emptied without operator intervention. These components can also allow most (if not all) of the compressed gas in the tank to be unloaded to the customer.

[0004] These components are constructed in a manner that they are assembled on trailers and / or cargo containers. These structures completely enclose the components. However, the structure provides enough space to approach each component so that on-site maintenance and repairs can be performed, and it is usually not necessary to leave the trailer off the road to go to a repair shop. The use of trailers allows the embodiments to be transported between locations. This feature is particularly useful for deploying these embodiments between remote locations in harsh climates and with limited access to shared facilities. In this regard, these components are configured to operate at ambient temperatures as low as -40°C under conditions where only natural gas is used as fuel, and to operate instruments (e.g., control valves), both of which are not available at remote locations. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Reference is now made briefly to the accompanying drawings, in which: Figure 1 depicts a schematic diagram of an exemplary embodiment of a system for reducing the pressure of a fluid formed in a tank; Figure 2 depicts a perspective view of a front portion of an exemplary embodiment of the system in assembled form; Figure 3 Depicted in assembled form Figure 2 Top view of the system Figure 4 Depicted in partially assembled form Figure 3 system; Figure 5 Depicted in partially assembled form Figure 2 A perspective view of the front of the system; Figure 6 Depicted in partially assembled form Figure 2 A perspective view of the rear of the system; Figure 7 Depicted in partially assembled form Figure 2 An elevation view of a first side portion of the system; Figure 8 Depicted in partially assembled form Figure 2 An elevation view of a second side of the system; and Fig. 9 A flow chart depicting an exemplary embodiment of a method for unloading compressed gas from a tank to a customer site is depicted.

[0006] Where applicable, like reference numerals denote identical or corresponding components and units throughout the several views, which are not drawn to scale unless otherwise expressly indicated. The embodiments disclosed herein may include elements that appear in one or more of the several views or in a combination of the several views. Furthermore, the methods are merely exemplary and may be modified by, for example, reordering, adding, removing, and / or changing individual stages. DETAILED DESCRIPTION

[0007] The following discussion describes embodiments that reduce the pressure of a compressed fluid. These embodiments are configured to regulate a fluid from a pressure of approximately 4000 psi to a pressure of approximately 80 psi. Other embodiments are within the scope of the disclosed subject matter.

[0008] Figure 1A schematic diagram of an exemplary embodiment of a system 100 for reducing the pressure of a compressed fluid is shown. The embodiment may be coupled to one or more storage tanks (e.g., a first storage tank 102 and a second storage tank 104). The tanks 102, 104 may hold a compressed fluid (typically a gas) at a storage pressure of typically about 4,000 psi or less. The system 100 may include a fluid circuit configured to reduce the pressure of the compressed fluid from the storage pressure. This feature may allow the fluid to be unloaded from the tanks 102, 104 to, for example, an auxiliary reservoir 106 at a customer site or facility. The auxiliary reservoir 106 may include a storage tank, a pipeline (or conduit), and / or a similar storage tank at a customer site that requires the fluid to be at a pressure lower than the fluid pressure in the tanks 102, 104.

[0009] The fluid circuit may have a plurality of components to adjust the fluid to a pressure suitable for the attached reservoir 106. These components may be located on a platform, which is generally shown as a virtual box indicated by the reference numeral 108. The platform 108 may have a structure that allows the system 100 to be transported between different sites and / or facilities. Suitable structures may include trailers or containers. These structures may include wheels that facilitate towing and movement, whether transported by train, truck or similar means of transportation. Moving from left to right on the platform 108, one embodiment of the fluid circuit may include a transfer unit 110 coupled to the tanks 102 and 104. The transfer unit 110 may include a valve component 112 to manage the flow of fluid from the tanks 102 and 104 to the downstream components in the fluid circuit. These downstream components may include a temperature regulating unit 114, a pressure reducing unit 116, and a flow meter 118. In the periphery, the system 100 may be coupled to a control unit 120, which has a controller 122 and one or more sensors (e.g., a first sensor 124). The controller 122 may be coupled to at least the valve member 112 and the flow meter 118 and to the first sensor 124. As such, the control unit 120 may operate components in the fluid circuit in response to changes in operating parameters that may occur when fluid is unloaded from the tanks 102, 104.

[0010] As noted above, the system 100 is configured to transfer fluid from the tanks 102, 104 to the auxiliary reservoir 106. These configurations can automatically operate in place of a human operator to couple the system 100 from one of the tanks 102, 104 to another. In use, the controller 122 can respond to changes in operating parameters to select the position (also referred to as a "state" or "condition") of the valve member 112. The selected position can correspond to a tank 102, 104 that is full and / or has fluid at a level sufficient to be unloaded to a customer. Examples of the first sensor 124 may include devices that are sensitive to pressure, temperature, and fluid flow, as well as other indicators that can be used to determine the position of the valve member. As shown, these devices can be coupled to the tanks 102, 104. Other embodiments can position the first sensor 124 at one or more locations downstream of the tanks 102, 104 in the fluid circuit.

[0011] The temperature regulating unit 114 may be configured to increase the temperature of the fluid from the tanks 102 and 104. These configurations may include a heat exchanger to facilitate indirect heat transfer between the fluids. The heat exchanger may be located upstream of the pressure reducing unit 116 and the flow meter 118. In one embodiment, the heat exchanger may increase the temperature of the fluid from the tanks 102 and 104 from a first temperature to a second temperature higher than the first temperature. The change in temperature may be about 220°F or less; for example, in use, the temperature regulating unit 114 may increase the temperature from about -40°F to about 180°F. The second temperature may determine the phase state of the fluid. Therefore, the present disclosure does not exclude the use of a cooler (and similar devices) that may cause the second temperature to be lower than the first temperature. However, it may be advantageous to keep the fluid in a gas phase rather than a liquid phase or a mixed phase (e.g., liquid and steam) for the second temperature. This feature may prevent the liquid from falling in other components of the fluid circuit downstream of the heat exchanger.

[0012] The pressure reducing unit 116 may be configured to reduce the pressure of the fluid from the tanks 102, 104. Figure 1 1 and 12. The plurality of stages are generally shown as a first stage 126 and a second stage 128. In each stage 126, 128, the decompression unit 116 may include throttling devices, such as valves and / or valve assemblies. These throttling devices may operate according to the Joule-Thomson effect to adiabatically expand the fluid.

[0013] In the first stage 126, the throttling device can reduce the fluid pressure from the first pressure to a second pressure lower than the first pressure. The device can cause a pressure drop of at least about 3,600 pounds per square inch or more. In one embodiment, the throttling device in the first stage 126 can adjust the fluid from about 4,000 pounds per square inch to about 400 pounds per square inch. An exemplary device as used in the first stage 126 may include a pressure regulator, which is generally a spring type or a pilot type. A spring type pressure regulator can help simplify the design. These types of devices are compatible with flows at high pressures but low flow rates (based on their low flow coefficients (Cv) relative to pilot type devices). In one embodiment, a pilot type pressure regulator can benefit the system 100 at the first stage 126. These types of regulators can provide more precise control of the second pressure under flow conditions. In addition, the pilot type design can minimize the "droop" and maintain the fluid flow rate in the fluid circuit in response to pressure changes that can be caused when the tanks 102, 104 are emptied over time. In one embodiment, the pilot-type design can maintain a flow rate of about 35,000 scfh in response to a pressure drop from an initial pressure of 4000 psi to about 200 psi of the fluid in the tanks 102, 104. In one example, the pressure regulator used in the first stage 126 can have a flow coefficient (Cv) in a range from about 4 to about 8, with an example of about 6.

[0014] The second stage 128 can be configured to further reduce the pressure of the fluid exiting the first stage 126. These configurations can use a control valve to reduce the pressure from the second pressure to a third pressure that is lower than the second pressure. The control valve can cause the pressure reduction to be at least about 320 psi or more. In one embodiment, the control valve of the second stage 128 can adjust the fluid from about 400 psi to about 80 psi. The third pressure can be in the range of about 50 psi to about 100 psi; however, the third pressure can be defined by the customer and / or the field facility.

[0015] The flow meter 118 may measure a property of the fluid. An example of a flow meter may be ultrasonic, but other types of flow meters may meet the needs of the system 100.

[0016] Figure 2 , 3 , 4, 5, 6, 7 and 8 show an exemplary structure for system 100. Figure 2 A perspective view of the front of the system 100 is depicted in assembled form. Figure 3 , 4 , 5 , 6 , 7 , and 7 depict system 100 in a partially assembled form.

[0017] Figure 2 An example of a system 100 configured to be transported between several different locations is depicted. The platform 108 may include a container structure 130 having components 132 that form ends (e.g., first end 134 and second end 136), sides (e.g., first side 138 and second side 140), a top 142, and a bottom 144. Due at least in part to the large size and load requirements of the platform 108, the components 132 may be made of steel, typically as plates that are fastened to one another using known and / or later developed fastening techniques; non-limiting examples of such techniques (at the time of this writing) include welding and bolting. The components 132 collectively form an enclosure that houses the components of the fluid circuit. The enclosure serves to protect the operating features of the system 100 from exposure to environmental conditions that may include extreme temperatures (both cold and hot) as well as precipitation, wind, dust, dirt, etc. As also shown, wheels 146 may be incorporated with the enclosure for transportation of the container structure 130 over road and / or rail. This feature is used for the mobility of the system 100 to facilitate access to remote locations or over rough, dirty roads and terrain.

[0018] Figure 3 A top view of the system 100 is provided. On the housing, the component 132 may form one or more door panels 150 to allow access to the interior of the container structure. The door panels 150 may be provided at various locations on the structure. Preferably, these locations provide access to different portions of the fluid circuit, as more fully indicated below.

[0019] Figure 4 A top view of the system 100 is also shown. Figure 3 ) and door panel 148( Figure 3 ) to show an exemplary configuration for the interior of the container structure 130. The outer shell has an interior cavity 148. The interior cavity 148 may form an area of ​​approximately 3,800 feet. 3 or otherwise at approximately 3,000 feet 3 To approximately 4,200 feet 3 In one embodiment, the container structure 130 may include a bisecting wall 152 across the volume, preferably coupled to the sides 138, 140. The bisecting wall 152 may separate the interior cavity 148 into at least two compartments (e.g., a first compartment 154 and a second compartment 156). Examples of the wall 152 may include a fireproof or fire-resistant material to serve as a barrier between the compartments 154, 156. As shown, the wall 152 may equally divide the volume between the compartments 154, 156, but this is not necessarily the case.

[0020] The compartments 154, 156 may house components of a fluid circuit. In the first compartment 154, the fluid circuit may have a network 158 having pipes, conduits, valves, and similar fluid conducting components throughout. The materials used for these components should be suitable for carrying the compressed fluid formed in the tanks 102, 104. The second compartment 156 houses the controller 122 and the heater 160. The exchange network 164 couples the heater 160 with the heat exchanger 162 to circulate the heat carrier medium (between the compartments 154, 156). The heater 160 may have an air inlet 166 and an exhaust port 168, which may be connected to the heater 160 through the door panel 148 ( Figure 3 ) extends out of the inner cavity 150. In one embodiment, the pipe network 158 is coupled to the heater 160 to distribute the compressed gas for use as a fuel.

[0021] The heater 160 may utilize a variety of structures. Examples of these structures may include electric heaters and thermal fluid heaters. Electric heaters provide a simple and efficient design. These devices do not require exhaust ports or vents to allow smoke or other exhaust gases and fluids to leave the inner cavity 148 of the housing. However, electric heaters require input power (e.g., electricity) to operate, which may be in short supply at the location even if available. Thermal fluid heating heaters can make the system 100 more robust for use in a wider range of locations. These types of heaters may include pumps to circulate the heat carrier medium (e.g., ethylene glycol, hot oil, water, etc.) through the (multiple) pipes of the exchange network 164. A boiler may also be necessary to increase the temperature of the heat carrier medium. The boiler can be used in the tanks 102, 104 ( Figure 1 ) of the facility or location (e.g., natural gas). Other configurations for heater 160 are also possible.

[0022] The heat exchanger 162 can utilize a variety of structures. Examples of these structures may include shell-and-tube designs or spiral tube designs as needed. With respect to the former, a shell-and-tube device may include a large pressure vessel having a tube bundle formed therein. The fluid flows through the tubes and flows on the tubes in the shell, effectively promoting the indirect heat exchange that occurs inside the device. These types of heat exchangers can be particularly costly because these devices often need to be customized for specific applications and require large lengths to maximize heat transfer. Spiral tubes or spiral tubes ("spiral tube heaters") are useful for addressing space limitations that may be formed on the platform 108 and particularly inside the inner cavity 148 of the shell. Other configurations for the heat exchanger 162 are also feasible.

[0023] The ductwork 158 may have components adjacent to the sides 138, 140 and the bisecting wall 152. These components may be secured to the member 132. Figure 4In the embodiment of the present invention, the location of the pipe network 158 can maximize the maintenance space 170 in the inner cavity 150 to allow ready access to the components of the system 100. At the first end 134, the pipe network 158 can have an inlet 172 and an outlet 174, each of which is connected to the tank 102, 104 ( Figure 1 ) and the dependent reservoir 106 ( Figure 1 ) is coupled. The inlet 172 may have a pair of conduits (e.g., a first conduit 176 and a second conduit 178) that are coupled to the tanks 102, 104, respectively. A hose may be used for this purpose. The conduits 176, 178 are also coupled to the transfer unit 110 ( Figure 1 ) coupling. Actuation of the transfer unit 110 via the controller 122 may allow the compressed fluid to flow from the tanks 102 , 104 into the pipe network 158 via at least one of the conduits 176 , 178 .

[0024] Figure 5 and Figure 6 The system 100 is depicted in partially exploded form from the front ( Figure 5 ) and rear ( Figure 6 ) is a perspective view as viewed from the outside. For clarity, portions such as some components 132 are removed. In the first compartment, the pipe network 158 may include one or more auxiliary components that may be useful for certain operational tasks including maintenance and repair. These auxiliary components may include one or more taps 180 distributed in various ways throughout the conduit. The taps 180 can lead fluid samples out of the pipe network 158. These samples can be useful for diagnosis and quality control. In one embodiment, the auxiliary components may include one or more isolation valves (e.g., a first isolation valve 182 and a second isolation valve 184) and a check valve 186. The isolation valves 182 and 184 can limit downstream flow as needed. The check valve 186 can prevent backflow of fluid from the outlet 174. In addition, the pipe network 158 may include a discharge line 188 to guide the fluid as a fuel for the heater 160.

[0025] like Figure 6 As best shown in FIG. 1 , the heater 160 fills a majority of the second compartment 156. The flame wall 152 serves as a protective barrier to isolate the gases flowing in the pipe network 158 of the first compartment 154 from any open flames, such as on the boiler of the heater 160.

[0026] Figure 7 and Figure 8 Show Figure 5 and Figure 6100 from the side. The exchange network 164 and the exhaust line 188 can penetrate the bottom 144 of the container structure 130. This configuration can maintain the integrity of the bisecting fire wall 152 and still allow gas to be transported between the compartments 154, 156. As noted above, this gas can ignite the boiler of the heater 160. This feature can reduce the risk of fire, effectively providing protection from injury to individuals working in either compartment 154, 156.

[0027] Fig. 9 A flow chart of an exemplary embodiment of a method 200 for transferring compressed gas from a storage tank to a storage reservoir under reduced pressure is shown. The method 200 may include providing a mobile trailer having compartments separated by a refractory wall at stage 202, the compartments including a first compartment and a second compartment. The method 200 may also include receiving gas at a first pressure in a first compartment of the mobile trailer at stage 204, and directing the gas through a valve operable to change the source of gas from the first tank to the second tank at stage 206. The method 200 may also include directing the gas through the first compartment using a pipe network at stage 208, which first increases the temperature of the gas and then reduces the pressure of the gas. The method 200 may include unloading gas at a second pressure lower than the first pressure from the first compartment at stage 210.

[0028] At stage 202, method 200 provides a mobile trailer. The mobile trailer may include a structure as discussed above in whole or in part. This stage may also include a stage for transporting the mobile trailer to a location and connecting the mobile trailer to a storage tank at the location.

[0029] At stage 204, the method 200 receives gas at the first compartment. This stage may include one or more additional stages for directing the gas from the compartment to one or more storage tanks holding compressed gas. Preferably, the method 200 may benefit from a pair or more storage tanks, because the method 200 may empty one of the tanks and continue to operate on the full tank to unload the gas (at a lower second pressure) when the end customer (e.g., a technician) removes the empty tank.

[0030] At stage 206, method 200 directs gas through a valve that can be changed between two (or more) storage tanks. Method 200 can benefit from "automation", such as sensors that generate signals in response to the level of compressed gas in the storage tanks. These signals can transmit data to a controller, which in turn can be configured to adjust the position of the valve in response to the level. In this way, when the first storage tank is empty, method 200 can switch the connection of the second storage tank to continue unloading into the reservoir.

[0031] At stage 208, method 200 directs the gas to increase the temperature and reduce the pressure. In this regard, method 200 may include one or more stages for flowing the compressed gas from the storage tank through a heat exchanger. This stage may increase or maintain the temperature of the fluid above some critical temperature for the compressed gas. At this critical temperature, the compressed gas may exhibit a phase composition of both vapor and liquid. Method 200 may also include one or more stages for subsequently flowing the fluid through a first throttling device and flowing the fluid through a second throttling device.

[0032] At stage 210, the method 200 may unload the gas at a lower second pressure from the first compartment. This stage may include one or more stages for measuring a parameter (e.g., flow rate) of the gas at the second pressure by, for example, flowing the gas through a flow meter or similar device. Prior to unloading, the method 200 may benefit from exhausting the gas from the first compartment to the second compartment in order to fire the boiler of the heater. The heater is useful for maintaining the operating temperature of the heat exchanger, thereby raising the temperature of the gas as noted above.

[0033] As used herein, an element or function recited in the singular and prefixed with "a" or "an" should be understood as not excluding the plural number of the element or function, unless such exclusion is explicitly stated. In addition, reference to "one embodiment" of the claimed invention should not be interpreted as excluding the existence of other embodiments that also include the recited features.

[0034] This written description uses examples to disclose the present embodiments, including the best mode, and also to enable those skilled in the art to practice the present embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of these embodiments is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that are insubstantially different from the literal language of the claims.

[0035] According to the foregoing discussion, embodiments of the present invention provide a mobile solution for transferring compressed gas from a high-pressure storage tank to a low-pressure storage reservoir. This mobile solution utilizes a structure that can be assembled on standard transportation and cargo containers for easy transportation to remote locations. In the field, the structure includes a fluid circuit that can be coupled to more than one storage tank. The fluid circuit can be equipped to change between storage tanks to maintain a constant or near-constant flow rate, thereby speeding up the unloading process, while utilizing gas to burn a boiler that heats the compressed gas to maintain its phase when the gas is transferred through the fluid circuit to be unloaded into the storage reservoir. In this regard, the following examples include certain elements or clauses, one or more of which can be combined with other elements and clauses describing the embodiments contemplated within the scope and spirit of the present disclosure.

Claims

1. A system comprising: a container forming an interior cavity, the container comprising a fire resistant wall dividing the interior cavity into a first compartment and a second compartment; a fluid circuit disposed in the first compartment, the fluid circuit comprising a heat exchanger and a decompression unit, the decompression unit forming a plurality of decompression stages to reduce the pressure of the incoming gas, the heat exchanger being disposed upstream of the plurality of decompression stages; as well as A heater is disposed in the second compartment and coupled to the fluid circuit to receive gas as a fuel source.

2. The system according to claim 1, characterized in that Also included is a structure for configuring the container for transport.

3. The system according to claim 1, characterized in that Also included is a transfer unit coupled to the fluid circuit, the transfer unit having connections for individually receiving incoming gas from the pair of tanks.

4. The system according to claim 3, characterized in that Also included is a valve disposed upstream of the heat exchanger and downstream of the transfer unit, the valve having at least two states, each state allowing incoming gas from one of the pair of containers to enter the fluid circuit.

5. The system according to claim 1, characterized in that Also included is a drain line coupling the fluid circuit to a heater, the drain line extending outside the container from the first compartment to the second compartment.

6. The system according to claim 1, characterized in that Also included is a pilot-type pressure regulator and control valve assembly, which are disposed in the fluid circuit as the plurality of pressure reducing stages.

7. The system according to claim 1, characterized in that The inner cavity has a width of at least 3,500 feet 3 The volume.

8. A mobile trailer, comprising: wall members, including the top, bottom, ends and sides of the container structure, the wall members forming an interior cavity; a fire barrier disposed in the interior cavity and coupled to the side, bottom, and top portions to separate the interior cavity into a first compartment and a second compartment; a fluid circuit disposed in the first compartment, the fluid circuit comprising, valve; a heat exchanger downstream of the valve; and a pair of throttling devices downstream of the heat exchanger; a heater disposed in the second compartment and coupled to the heat exchanger, the heater comprising a boiler; and The boiler is coupled to a discharge line of the fluid circuit.

9. The mobile trailer according to claim 8, characterized in that: The exhaust line bypasses the refractory wall.

10. The mobile trailer according to claim 8, characterized in that: The drain line extends through a bottom of each of the first compartment and the second compartment.

11. The mobile trailer according to claim 8, characterized in that: The heat exchanger includes a coiled tube.

12. The mobile trailer according to claim 8, characterized in that: The pair of throttling devices include pilot-type pressure regulators.

13. The mobile trailer according to claim 12, characterized in that: The inner cavity has a width of at least 3,500 feet 3 The volume.

14. The mobile trailer according to claim 8, characterized in that: The pair of throttling devices are configured to reduce the gas pressure from 4,000 psi to less than 100 psi at a flow rate of at least 35,000 scfh.

15. A method comprising: providing a mobile trailer having compartments separated by a fireproof wall, the compartments comprising a first compartment and a second compartment; receiving gas at a first pressure in the first compartment of the mobile trailer; directing the gas through the first compartment using a pipe network to first increase the temperature of the gas and then reduce the pressure of the gas; and The gas at a second pressure lower than the first pressure is unloaded from the first compartment.

16. The method according to claim 15, characterized in that Also includes: The gas is discharged from the first compartment to the second compartment to cause the boiler of the heater to burn, thereby heating the gas in the first compartment.

17. The method according to claim 16, characterized in that Also includes: The gas is directed outside of the mobile trailer to bypass a fire wall separating the first compartment and the second compartment.

18. The method according to claim 16, characterized in that Also includes: An exhaust port for the boiler is provided from the second compartment.

19. The method according to claim 15, characterized in that Also includes: The gas is directed through a valve operable to change the source of the gas from the first tank to the second tank.

20. The method according to claim 15, characterized in that Also includes: The flow rate of the gas at the second pressure is measured.

Images