Reducing pressure of compressed gas from a storage tank

A system that can offload compressed gas from a storage tank to a customer site. The system can have a fluid circuit that is configured to fit within a container structure, like a trailer, for mobility to remote locations. This fluid circuit can include a transfer unit to automatically switch between tanks. The transfer unit can couple with a heat exchanger. Downstream of the heat exchanger, the fluid circuit can reduce pressure of fluid from the tanks through multiple pressure reduction stages. Each of the pressure reduction stages can include a throttling device, for example, a pilot-type fluid regulator and a control valve assembly. The throttling device may be selected to maintain flow of fluid at least at, e.g., 35,000 scfh, in accordance with pressure drops in the incoming fluid from the tanks.

BACKGROUND

Delivery of hydrocarbons may utilize tanks that transit by truck, ship, and rail. These tanks can carry large amounts of compressed gas under very high pressure. However, there is often a mismatch between the pressure of the gas during transit and the pressure that the customer requires to unload the compressed gas from the tanks.

SUMMARY

The subject matter of this disclosure relates generally to unloading of compressed gas. The embodiments herein can distribute gas found at “high” pressure in transit tanks (e.g., tube trailers) to customer designated repositories. These repositories are often configured only to receive gas at “low” pressure. As noted more below, some embodiments may integrate components that can satisfy the pressure drop from tank to customer repository. These components may maintain the gas as vapor to avoid two-phase flow that can frustrate accurate and reliable measure of properties (e.g., temperature, pressure, flow, etc.) of fluid that disperses to the customer. The components can also automate operation to allow multiple tanks to empty without intervention by an operator. The components can further permit most, if not all, of the compressed gas in the tanks to offload to the customer.

The components are configured in a way to fit on-board a trailer and/or cargo container. These configurations fully enclose the components. However, the configuration provides sufficient room to access each component in order to perform maintenance and repair onsite, often without the need to take the trailer off the road to a repair facility. Use of the trailer permits the embodiments to transit between locations. This feature is useful, particularly, to deploy the embodiments among remote locations found in harsh climates and with limited access to utilities. In this regard, the components are configured to operate in ambient temperatures down to −40° C. with only natural gas for use as fuel and to operate instrumentation (e.g., control valves), both of which may be unavailable at the remote locations.

Where applicable like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated. The embodiments disclosed herein may include elements that appear in one or more of the several views or in combinations of the several views. Moreover, methods are exemplary only and may be modified by, for example, reordering, adding, removing, and/or altering the individual stages.

DETAILED DESCRIPTION

The discussion below describes embodiments to reduce pressure of compressed fluid. These embodiments are configured to condition the fluid from a pressure of approximately 4000 psig to a pressure of approximately 80 psig. Other embodiments are within the scope of the disclosed subject matter.

FIG. 1illustrates a schematic diagram of an exemplary embodiment of a system100to reduce pressure of a compressed fluid. The embodiment can couple with one or more storage tanks (e.g., a first storage tank102and a second storage tank104). The tanks102,104can hold compressed fluid, typically gas, at a storage pressure that is often at approximately 4,000 psig or less. The system100may include a fluid circuit with components that are configured to reduce pressure of the compressed fluid from the storage pressure. This feature can allow the fluid to offload from the tanks102,104to a collateral repository106at, for example, a customer site or facility. This collateral repository106may embody a holding tank, pipe (or conduit), and/or like receptacle at the customer site that requires the fluid to be at lower pressures relative to the pressure of the fluid in the tanks102,104.

The fluid circuit can have a number of components to condition the fluid to a pressure that is appropriate for the collateral repository106. These components may reside on a platform, shown generally as the phantom box enumerate by the numeral108. The platform108can have a structure that permits the system100to transit among different sites and/or facilities. Suitable structures may embody a trailer or a container. These structures can include wheels that ease towing and mobility, whether by train, truck, or like vehicular transportation. Moving from left to right on the platform108, one implementation of the fluid circuit may include a transfer unit110that couples with the tanks102,104. The transfer unit110may include a valve member112to manage flow of fluid from the tanks102,104to downstream components in the fluid circuit. These downstream components may include a temperature conditioning unit114, a pressure reduction unit116, and a flow meter118. Peripherally, the system100may couple with a control unit120that has a controller122and one or more sensors (e.g., a first sensor124). The controller122may couple with at least the valve member112and the flow meter118, as well as with the first sensor124. In this way, the control unit120can operate the components in the fluid circuit in response to variations in operating parameters that may occur as the fluid offloads from the tanks102,104.

As noted above, the system100is configured to transfer fluid from tanks102,104to the collateral repository106. These configurations may operate autonomously in lieu of manual operators that would couple the system100from one of the tanks102,104to the other. In use, the controller122can respond to changes in the operating parameters to select a position (also “state” or “condition”) for the valve member112. The selected position may correspond with the tank102,104that is full and/or that has fluid at levels that is sufficient to offload to the customer. Examples of the first sensor124may include devices that are sensitive to pressure, temperature, and fluid flow, among other indicators that might useful to determine the position for the valve member. These devices may couple with tanks102,104, as shown. Other implementations may position the first sensor124in the fluid circuit at one or more positions downstream of the tanks102,104.

The temperature conditioning unit114can be configured to raise temperature of fluid from the tanks102,104. These configurations may embody a heat exchanger to promote thermal transfer indirectly between fluids. The heat exchanger can reside upstream of the pressure reduction unit116and the flow meter118. In one implementation, the heat exchanger can raise the temperature of the fluid from the tanks102,104from a first temperature to a second temperature that is greater than the first temperature. The change in temperature may be approximately 220° F. or less; for example, in use, the temperature conditioning unit114can raise the temperature from approximately −40° F. to approximately 180° F. The second temperature may determine the phase of the fluid. So this disclosure does not foreclose use of a cooler (and like devices) that could cause the second temperature to be lower than the first temperature as well. However, it may be advantageous for the second temperature to maintain the fluid in vapor phase, rather than in liquid phase or mixed phase (e.g., liquid and vapor). This feature can prevent liquid dropouts in the other components of the fluid circuit that are downstream of the heat exchanger.

The pressure reduction unit116can be configured to reduce the pressure of the fluid from the tanks102,104. These configurations can utilize multiple stages, shown generally inFIG. 1as a first stage126and a second stage128. In each of the stages126,128, the pressure reduction unit116may include a throttling device, like a valve and/or valve assembly. These throttling devices can operate in accordance with Joule-Thompson effect to adiabatically expand the fluid.

At the first stage126, the throttling device may reduce the pressure of the fluid from a first pressure to a second pressure that is lower than the first pressure. This device may cause a pressure drop of at least approximately 3,600 psig or more. In one implementation, the throttling device in the first stage126can condition the fluid from approximately 4,000 psig to approximately 400 psig. Exemplary devices for use as in this first stage126can include pressure regulators, often of a spring-type or pilot-type. The spring-type pressure regulator may help simplify the design. These types of devices may be compatible with flow at high pressure but lower flow rates (based on their low flow co-efficient (Cv) relative to pilot-type devices). In one implementation, the pilot-type pressure regulator may benefit the system100at the first stage126. These types of regulators may provide more accurate control of the second pressure under flowing conditions. Moreover, the pilot-type design can minimize “droop” and maintain flowrate of fluid in the fluid circuit in response to pressure changes that may result as the tanks102,104empty over time. In one implementation, the pilot-type design can maintain flow rate at approximately 35,000 scfh in response to pressure drop of the fluid in the tanks102,104from an initial pressure of 4000 psig to approximately 200 psig. In one example, the pressure regulator for use in the first stage126may have a flow coefficient (Cv) that is in a range of from approximately 4 to approximately 8, with one example at approximately 6.

The second stage128may be configured to further reduce the pressure of the fluid that exits the first stage126. These configurations may use a control valve to drop the pressure from the second pressure to a third pressure that is lower than the second pressure. The control valve may cause the pressure to drop by at least approximately 320 psig or more. In one implementation, the control valve in the second stage128can condition the fluid from approximately 400 psig to approximately 80 psig. The third pressure may be in a range of from approximately 50 psig to approximately 100 psig; however, this third pressure may be defined by the customer and/or site facilities.

The flow meter118can measure properties of the fluid. Examples of the flow meter may be ultrasonic, although other types of flow meters may suffice for the system100.

FIG. 2depicts an example of the system100that is configured to transit among several different locations. The platform108can include a container structure130with members132that form ends (e.g., a first end134and a second end136), sides (e.g., a first side138and a second side140), a top142, and a bottom144. Due at least in part to the large size and duty requirements on the platform108, the members132can be made of steel, often as plates that fasten with one another using known and/or after-developed fastening techniques; non-limiting examples of these techniques (at the present writing) include welding and bolting. Collectively, the members132form an enclosure that houses the components of the fluid circuit. The enclosure serves to protect the working features of the system100from exposure to ambient conditions, which may include excessive temperatures (both cold and warm) as well as precipitation, wind, dust, dirt, and the like. As also shown, wheels146may integrate with the enclosure for transit of the container structure130over road and/or rail. This feature serves the mobility of the system100to provide access to remote locations or over rough, unkempt roads and terrain.

FIG. 3provides a top view of the system100. On the enclosure, the members132may form one or more door panels150to allow access to the interior of the container structure. The door panels150may be disposed in various locations on the structure. Preferably, these locations afford access to different parts of the fluid circuit, as noted more below.

FIG. 4also illustrates the top view of the system100. Some parts including the top142(FIG. 3) and door panels148(FIG. 3) are absent to visualize an exemplary configuration for the inside of the container structure130. The enclosure has an interior cavity148. This interior cavity148can form a volume that is approximately 3,800 ft3or, otherwise, in a range from approximately 3,000 ft3to approximately 4,200 ft3. In one implementation, the container structure130may include a bisecting wall152that traverses the volume, preferably coupling with the sides138,140. The bisecting wall152can separates the interior cavity148into at least two compartments (e.g., a first compartment154and a second compartment156). Examples of the wall152can comprise fire or flame resistant material to operate as a barrier between the compartments154,156. As shown, the wall152may split the volume equally between the compartments154,156, but this does not have to be the case.

The compartments154,156can house components of the fluid circuit. In the first compartment154, the fluid circuit can have a piping network158with pipes, conduits, valves, and like fluid conducting components dispersed throughout. Materials for these components should be suitable to carry the compressed fluid found in tanks102,104. The second compartment156houses the controller122and a heater160. An exchange network164couples the heater160with a heat exchanger162to circulate heating medium (between the compartments154,156). The heater160can have an intake166and exhaust168that may extend out of the interior cavity150via door panels148(FIG. 3). In one implementation, piping network158couples with the heater160to disperse compressed gas for use as fuel.

The heater160may leverage a variety of constructions. Examples of these constructions may embody electric heaters and thermal fluid heating heaters. Electric heaters afford a simple and efficient design. These devices require no exhaust or venting that would allow fumes or other waste gas and fluids to exit the interior cavity148of the enclosure. However, electric heaters need input power (e.g., electricity) to operate, which may be in short supply at the location, if available at all. Thermal fluid heating heaters may make the system100more robust to serve a broader range of locations. These types of heaters may include a pump to circulate the heating medium (e.g., glycol, thermal oil, water, etc.) through the tube(s) of the exchange network164. A boiler may be necessary to raise the temperature of the heating medium as well. The boiler may use fuel (e.g., natural gas) that is available at the facility and/or location of the tanks102,104(FIG. 1). Other configurations for the heater160may also be feasible as well.

The heat exchanger162may leverage a variety of constructions. Examples of these constructions may embody shell-and-tube designs or spiral tube designs, as desired. As to the former, shell-and-tube devices may comprise a large pressure vessel with bundles of tubes found therein. Fluid flow through the tubes and over the tubes in the shell, effectively promoting indirect heat exchange to occur inside of the device. These types of heat exchanger may be particularly cost prohibitive because these devices often require customization for use in the particular application and, moreover, require extensive length to maximize heat transfer. Spiral or helical tubes (“spiral tube heat exchangers”) are useful to address space constraints that might be found on-board the platform108and, particularly, inside of the interior cavity148of the enclosure. Other configurations for the heat exchanger162may also be feasible as well.

The piping network158may have components that are disposed proximate the sides138,140and the bisecting wall152. These components may secure to the members132. InFIG. 4, the position for the piping network158can maximize a maintenance space170in the interior cavity150to allow ready access to the components of the system100. At the first end134, the piping network158can have an inlet172and an outlet174, one each to couple with tanks102,104(FIG. 1) and the collateral repository106(FIG. 1). The inlet172can have a pair of conduits (e.g., a first conduit176and a second conduit178) that couple with the tanks102,104, respectively. Hoses might be useful for this purpose. The conduits176,178also couple with the transfer unit110(FIG. 1). Actuation of the transfer unit110via controller122may allow the compressed fluid to flow from tanks102,104into the piping network158via at least one of the conduits176,178.

FIGS. 5 and 6depict a perspective view of the system100in partially-exploded form from the front (FIG. 5) and the back (FIG. 6). Parts like some members132are removed for clarity. In the first compartment, the piping network158may include one or more collateral components that might be useful for certain operative task including maintenance and repair. These collateral components may include one or more taps180dispersed variously throughout the conduits. The taps180can direct samples of the fluid out of the piping network158. These samples may be useful for diagnostics and quality control. In one implementation, the collateral components may include one or more isolation valves (e.g., a first isolation valve182and a second isolation valve184) and a check valve186. The isolation valves182,184can restrict downstream flow, as necessary. The check valve186can prevent backflow of fluid from the outlet174. Further, the piping network158may include a bleed-off line188to direct fluid as fuel for the heater160.

As best shown inFIG. 6, the heater160fills up a majority of the second compartment156. The firewall152operates as the protective barrier to separate gas that flows in the piping network158of the first compartment154from any open flame on, for example, the boiler of the heater160.

FIGS. 7 and 8show an elevation view of the system100ofFIGS. 5 and 6from the sides. The exchange network164and the bleed-off line188may penetrate the bottom144of the container structure130. This configuration can retain the integrity of the bisecting firewall152and still allow gas to transit between compartments154,156. As noted above, this gas may fire the boiler of the heater160. This feature can reduce risks of fire, effectively offering protection to individuals working in either compartment154,156from injury.

FIG. 9illustrates a flow diagram of an exemplary embodiment of a method200to transfer compressed has from storage tanks to repositories at reduced pressure. The method200can include, at stage202, providing a mobile trailer with compartments separated by a fire-resistant wall, the compartments comprising a first compartment and a second compartment. The method200can also include, at stage204, receiving gas at a first pressure in the first compartment of the mobile trailer and, at stage206, directing the gas through a valve operable to change a source of the gas from a first tank to a second tank. The method200may further include, at stage208, directing the gas through the first compartment using a piping network that first raises the temperature of the gas and then reduces the pressure of the gas. The method200may include, at stage210, offloading the gas from the first compartment at a second pressure that is lower than the first pressure.

At stage202, the method200provides the mobile trailer. This mobile trailer may comprises the structure, in whole or in part, as discussed above. This stage may also include stages for transporting the mobile trailer to a location and connecting the mobile trailer to storage tanks at the location.

At stage204, the method200receives the gas at the first compartment. This stage may include one or more additional stages for directing the gas from to one or more storage tanks that hold compressed gas. Preferably, the method200may benefit from a pair of storage tanks, or more, because the method200can empty one of the tanks and continue to operate on the full tank to offload the gas (at a lower, second pressure) as an end user (e.g., a technician) removes the empty tank.

At stage206, the method200directs the gas through a valve that can change between the two (or more) storage tanks. The method200may benefit from “automation,” for example, sensors that generate signals in response to a level of the compressed gas in the storage tanks. These signals may transmit data to a controller, which in turn may be configured to regulate the position of the valve in response to the level. In this way, as a first storage tank runs empty, the method200can switch over connection of a second storage tank to continue to offload to the repository.

At stage208, the method200directs the gas to increase temperature and reduce pressure. In this regard, the method200may include one or more stages for flowing the compressed gas from the storage tanks through a heat exchanger. This stage can raise or maintain the temperature of the fluid above certain critical temperatures for the compressed gas. At this critical temperature, the compressed gas may exhibit a phase composition that is both vapor and liquid. The method200may 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.

At stage210, the method200may offload the gas from the first compartment at the lower second pressure. This stage may include one or more stages for measuring parameters (e.g. flow rate) of the gas at the second pressure, for example, by flowing the gas through a flow meter or like device. Prior to offloading, the method200may benefit from bleeding-off gas from the first compartment to the second compartment to fire a boiler of a heater. This heater is useful to maintain an operating temperature of the heat exchanger, thus increasing the temperature of the gas as noted above.

As used herein, an element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

In light of the foregoing discussion, the embodiments herein offer a mobilized solution to transfer compressed gas from a high pressure storage tank to a lower pressure repository. This mobilized solution leverages structure that may fit onto standard transport and cargo containers for easy transport to remote locations. Onsite, the structure includes a fluid circuit that can couple to more than one storage tank. This fluid circuit can be equipped to offloading procedure, while at the same time leveraging the gas to fire a boiler that heats the compressed gas to maintain its phase as the gas transits the fluid circuit to offload into the repository. In this regard, the examples below include certain elements or clauses one or more of which may be combined with other elements and clauses describe embodiments contemplated within the scope and spirit of this disclosure.