Cryogenic container with reserve pressure building chamber

A system for dispensing cryogenic liquid includes a container defining an interior with a partition dividing the interior into primary and reserve chambers. Cryogenic liquid within the primary chamber is separated from cryogenic liquid in the reserve chamber. The partition provides a headspace cornrnurrrcation passage. A primary pressure building circuit has an inlet selectively in liquid communication with the primary chamber and an outlet in fluid communication with the headspaces of the primary and reserve chambers. A reserve pressure building circuit has an inlet selectively in liquid communication with the reserve chamber and an outlet in fluid communication with the headspaces of the primary and reserve chambers. An equalizing circuit is selectively in liquid communication with the primary and reserve chambers. A dispensing line is selectively in liquid communication with the primary chamber.

FIELD OF THE INVENTION

The present disclosure relates generally to cryogenic containers and, in particular, to a cryogenic container with a reserve pressure building chamber for dispensing residual amounts of liquid cryogen from the container.

BACKGROUND

Cryogenic fluids, that is, fluids having a boiling point generally below −150° C. at atmospheric pressure, are used in a variety of applications, such as mobile and industrial applications. Cryogenic fluids are typically stored as liquids to reduce volume and thus permit containers of more practical and economical design to be used. The liquids are often stored in double-walled bulk tanks or containers with a vacuum between the walls of inner and outer vessels as insulation to reduce heat transfer from the ambient environment into the cryogenic liquid.

During dispensing, the tank is typically pressurized so that the cryogenic liquid is driven from the tank. Tank pressure is often increased using a pressure building circuit that is common on many stationary cryogenic cylinders. These circuits function by using vapor and liquid head pressure to feed liquid cryogen into a pressure building coil or other type of vaporizer. Upon vaporization of the liquid, its volume expands and the resulting gas is routed to the vapor space above the liquid cryogen, building a head of vapor pressure above the liquid phase in the tank.

Most mobile cryogenic liquid containers are mounted horizontally, that is, the longitudinal axis of the tank is generally horizontal or parallel to the surface of the ground. This permits the containers to be transported in ISO specification shipping containers and provides a space efficient profile for vehicle fuel tanks (such as for liquid natural gas powered vehicles). In addition, the horizontal orientation permits the containers to pass through tunnels and under bridges, power lines and the like when transported by a vehicle.

Horizontal cryogenic storage vessels, however, do not maintain a differential pressure sufficient to drive liquid through the pressure building coil at low liquid levels, such as when the tank is nearly empty. More specifically, with reference toFIG. 1a, a horizontal tank10contains a supply of cryogenic liquid12with a vapor headspace14above it. A cryogenic liquid dispensing line16is connected to the bottom of the tank and features a dispensing valve18. The distal end of the dispensing line16is provided with a nozzle or connector22that connects to a use or storage device. A vent line24features a vent valve26and is in fluid communication with the headspace14via spraybar28. A pressure building line32is provided with a pressure building valve34and a pressure building coil36. The outlet of the pressure building coil is provided with a check valve38and also communicates with the headspace via spraybar28.

In operation, the tank10is filled to maximum capacity with cryogenic liquid12, as illustrated inFIG. 1a. To dispense the liquid, the connector22is connected to a use or storage device. The vent valve26may be opened to equalize the pressure between a tank of the use or storage device and the tank10, and is then closed.

The pressure building valve34is then opened. Due to the pressure at the bottom of the tank, which results from the vapor pressure in the headspace14in combination with the liquid head of the tank, liquid cryogen travels through line32to pressure building coil36where it is vaporized. The resulting vapor travels through the check valve38and into the headspace14through the spraybar28so that the tank is pressurized.

When the tank reaches the desired pressure, the dispensing valve18is opened and liquid cryogen travels through line16, connector22and into the use or storage device.

As illustrated inFIG. 1b, the liquid level of the tank will drop due to the withdrawal of liquid from the tank. This causes an increase in the volume of the headspace14and a decrease in the liquid head provided by the cryogenic liquid12. As a result, there is insufficient pressure at the bottom of the tank to drive the remaining amount of liquid to the pressure building coil36, and sufficient pressure building within the tank for dispensing can no longer be accomplished. The liquid heel, that is, the residual liquid in the tank, therefore cannot be dispensed through line16.

The above issue is problematic for a couple of reasons. First, the liquid cryogen remaining in the tank is wasted. Second, over time, the liquid cryogen remaining in the tank will vaporize and increase the tank internal pressure. If a long time passes during storage or transport, such as when the tank is shipped back to the source overseas for refilling, the tank may need to be vented during transport. This is undesirable, especially when a large number of tanks need to be vented.

SUMMARY

In one aspect, a system for dispensing cryogenic liquid includes a container defining an interior. A partition divides the interior into a primary chamber and a reserve chamber, with each of the primary and reserve chambers configured to contain a cryogenic liquid with a headspace above the cryogenic liquid. The cryogenic liquid within the primary chamber is separated from the cryogenic liquid in the reserve chamber. The partition is also configured to provide a headspace communication passage so that the headspace of the primary chamber is in fluid communication with the headspace of the reserve chamber. A primary pressure building circuit has an inlet selectively in liquid communication with a bottom portion of the primary chamber and an outlet in fluid communication with the headspaces of the primary and reserve chambers of the tank. A reserve pressure building circuit has an inlet selectively in liquid communication with a bottom portion of the reserve chamber and an outlet in fluid communication with the headspaces of the primary and reserve chambers of the tank. An equalizing circuit is selectively in liquid communication with the primary and reserve chambers. A dispensing line is selectively in liquid communication with the bottom of the primary chamber.

In another aspect, a container for dispensing cryogenic liquid includes a vessel defining an interior with a partition dividing the interior into a primary chamber and a reserve chamber. Each of the primary and reserve chambers is configured to contain a cryogenic liquid with a headspace above the cryogenic liquid, where the cryogenic liquid within the primary chamber is separated from the cryogenic liquid in the reserve chamber. The partition is also configured to provide a headspace communication passage so that the headspace of the primary chamber is in fluid communication with the headspace of the reserve chamber. A primary cryogenic liquid passage and a liquid dispensing outlet are positioned in a bottom portion of the primary chamber. A reserve cryogenic liquid passage is positioned in a bottom portion of the reserve chamber.

In yet another aspect, a method of dispensing a cryogenic liquid includes the steps of separately storing the cryogenic liquid within a primary chamber and a reserve chamber of a container, where the cryogenic liquid stored in the primary and reserve chambers share a common headspace, vaporizing cryogenic liquid from the primary chamber and using a resulting gas to pressurize the common headspace, dispensing cryogenic liquid from the primary chamber and vaporizing cryogenic liquid from the reserve chamber and using a resulting gas to pressurize the common headspace.

DETAILED DESCRIPTION OF EMBODIMENTS

While the invention is described below in terms of a tank containing cryogenic liquid, it may be used for pressurizing other types of containers and vessels.

An embodiment of a tank constructed in accordance with the invention is indicated in general at40inFIG. 2a. The tank includes an inner vessel42surrounded by an outer vessel or jacket44with a space46therebetween that may be vacuum insulated. Each of the inner and outer vessels feature a cylindrical cross section and are provided with dome shaped end caps. Alternative container shapes may be used. In addition, the container may instead be single-walled or include additional jackets. As illustrated inFIG. 2b, the longitudinal axis of the tank, indicated at48, is generally horizontal or parallel to the ground or other supporting surface. As a result, the tank40is a horizontal tank.

The tank contains a supply of cryogenic liquid52with a vapor headspace54above it.

A cryogenic liquid dispensing line56is connected to the bottom of the tank via a liquid dispensing outlet and features a dispensing valve58. The distal end of the dispensing line56is provided with a nozzle or connector62that connects to a use or storage device. A vent line64features a vent valve66and is in fluid communication with the tank headspace54via a spraybar68.

A primary pressure building circuit, indicated in general at70, includes primary pressure building line72and a primary pressure building valve74. A reserve pressure building circuit, indicated in general at80, includes a reserve pressure building line82provided with a reserve pressure building valve84. As will be described in greater detail below, both of these pressure building lines extend between the bottom of the tank40and a junction86. An equalizing valve88is positioned between the junction86and the inlet of a pressure building coil92. The outlet of the pressure building coil92is provided with a check valve94and also is in fluid communication with the headspace54of the tank via spraybar68.

While the primary and reserve pressure building circuits share a pressure building coil92inFIGS. 2a-2c, they may instead be provided with separate dedicated pressuring building coils. In addition, while a pressure builder coil is illustrated, other types of vaporizers known in the art may be used instead.

The interior of the tank40is provided with a partition100. As illustrated inFIG. 3, the partition100is secured to the interior surface of the inner vessel42and a top edge102of the partition is spaced from the top of the tank so that a headspace communication passage103is formed. As a result, the interior of the tank40is divided into a primary chamber104(to the left of the partition100inFIG. 2a) and a reserve chamber106(to the right of the partition100inFIG. 2a). While liquid sides of the primary and reserve chambers are isolated from one another, the headspaces of the chambers are in fluid communication with one another due to the partition extending only part way up within the tank interior. As a result, the headspaces of the primary and reserve chambers form a common headspace and the partition100is not a pressure barrier and does not create an additional pressure vessel.

In place of the space provided between the top edge of the partition and the top of the tank (103inFIG. 3), the partition could extend all of the way to the top of the tank and feature one or more openings positioned in the headspace of the tank so as to form the headspace communication passage. Furthermore, the headspace communication passage may feature any construction that permits the headspaces of the primary and reserve chambers104and106to be in fluid communication with one another.

The inlet to the primary pressure building circuit70is in liquid communication with the bottom of the primary chamber104of the tank via a primary cryogenic liquid passage, while the inlet to the reserve pressure building circuit80is in liquid communication with the bottom of the reserve chamber106of the tank via a reserve cryogenic liquid passage.

In operation, the tank40is initially filled to maximum capacity with cryogenic liquid52, as illustrated inFIG. 2a. All of the illustrated valves are initially closed. To dispense the liquid, the connector62is connected to a use or storage device. The vent valve66may be opened to equalize the pressure between a tank of the use or storage device and the tank40, and is then closed.

It should be noted that the tank40may also be refilled when the connector62is connected to a source of pressurized liquid and valve66is opened (with the remaining valves closed). The liquid entering the tank40through the spraybar68collapses the vapor pressure in the headspace54to permit the liquid to enter the tank.

The primary pressure building valve74and the equalizing valve88are then opened. Due to the pressure at the bottom of the tank, which results from the vapor pressure in the headspace54in combination with the liquid head in the primary chamber104of the tank, liquid cryogen travels through the primary pressure building line72to the pressure building coil92where it is vaporized. The resulting vapor travels through the check valve94and into the headspace54through the spraybar68so that the tank is pressurized.

When the tank reaches the desired pressure, the dispensing valve58is opened and liquid cryogen travels from the bottom of the primary chamber104of the tank through line56, connector62and into the use or storage device. The liquid level of the primary chamber104of the tank will drop due to the withdrawal of liquid from the tank.

With reference toFIG. 2b, as liquid is withdrawn from the primary chamber104of the tank and the level nears empty, there will be insufficient pressure to force the liquid from the primary chamber to the pressure building coil92.

At this point, the dispensing valve58and the primary pressure building valve74are closed and the reserve pressure building valve84of the reserve pressure building supply circuit is opened. The equalizing valve88remains open. Due to the liquid head in the reserve chamber106, and what pressure is left in the headspace54of the tank, liquid from the bottom of the reserve chamber106of the tank is driven through the reserve pressure building line82to the pressure building coil92, vaporized, and directed to the headspace54of the tank via spray bar68so as to build pressure therein.

Once the tank40has reached a sufficient pressure to dispense, the primary and reserve compartments104and106of the tank are equalized by closing the equalizing valve88and opening the primary pressure building valve74(the reserve pressure building valve84remains open). As a result, as illustrated inFIG. 2c, the liquid levels within the primary and reserve chambers104and106of the tank equalize as liquid flows through lines72and82. As a result, the lines72and82and valves74and84form an equalizing circuit.

In an alternative embodiment, the equalizing circuit may be formed as a separate line running between the bottoms of the primary and reserve chambers with a valve positioned therein. In such an embodiment, the equalizing valve88ofFIGS. 2a-2ccould be omitted.

The dispensing valve58is then opened (equalizing valve88remains closed), and liquid dispensing resumes from the primary chamber104. As liquid is dispensed from the primary chamber104, and the liquid level therein drops, liquid from the reserve chamber106flows through lines82and72into the primary chamber104and is dispensed. As a result, both the primary and reserve chambers104and106of the tank40are either emptied or nearly emptied of liquid.

The valves ofFIGS. 2a-2ccould be manipulated manually by a user to perform the above process. The user would need to monitor pressure gauges positioned within the bottoms of the primary and reserve chambers104and106to determine when pressures are sufficient for dispensing.

Alternatively, the system and process ofFIGS. 2a-2ccould be automated by providing pressure sensors in the bottoms of the primary and reserve chambers104and106with a programmable controller connected to the pressure sensors. In such an embodiment, the valves ofFIGS. 2a-2cwould be automated and actuated by the controller in response to the pressure sensed by the pressure sensors. Alternative suitable automatic control systems known in the art could be implemented as well.

Locating the reserve chamber106at the end of the tank, as illustrated inFIGS. 2a-2c, is efficient and economical in that it facilitates running piping and gauges to the reserve chamber (i.e. through the end wall or dome of the tank). Nevertheless, the reserve chamber could be positioned anywhere within the interior of the tank so long as a column of liquid is provided.

The system ofFIGS. 2a-2c, or other embodiments of the system, could use the reserve chamber to supplement the dispensing while dispensing from the primary chamber. More specifically, the reserve pressure building valve84ofFIG. 2acould be opened while the primary pressure building valve74and the equalizing valve88are open, and before the liquid level reaches the level ofFIG. 2b.

In summary, adding a partition inside the inner vessel allows the container to maintain a sufficient column of liquid in the reserve chamber, providing the differential pressure to drive liquid through a pressure building coil or other vaporizer at low liquid levels in the primary chamber of the container.

This solution could be applied to any horizontal cryogenic container where pressure building capabilities at low liquid levels are required and the container needs to be emptied completely.

While the preferred embodiments of the disclosure have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the disclosure, the scope of which is defined by the following claims.