Patent Application
20070151621
The field of cryogenics requires liquefied gases when conducting experiments and observations. The two types of liquefied gases used in most cryogenic applications are liquid helium and liquid nitrogen (LN2). In order to store LN2, for example, special containers known as Dewar flasks (Dewars) are used. For practical purposes, the Dewars used are generally about six feet tall and three feet in diameter. The Dewar is designed to provide very good thermal insulation. In the case of storing LN2, the leakage of heat into the extremely cold interior of the flask results in a slow “boiling-off” of the LN2. A pressure relief valve is provided to prevent pressure from building up. The excellent insulation of the Dewar results in the LN2 lasting a long time without the need for expensive refrigeration equipment.
When filling the Dewar with LN2, determining when the Dewar is full is a difficult task that requires constant monitoring. When the Dewar is overfilled, the LN2 will continue to pour out of a relief vent and is wasted. This waste of LN2 is expensive and dangerous. Inhaling LN2 causes minor to severe breathing difficulty, which is a safety hazard to cryogenic lab personnel. Additionally, determining the level of remaining LN2 is difficult when traditional level gauges are mounted on top of the Dewar. While in use, the top of the Dewar is often covered with frost, rendering the gauge difficult to read and subject to measurement inaccuracies.
Economics also play a role in the storage of liquefied gases. The ability to provide a readily-available source of liquefied gas improves the chance of successful studies in a cryogenic lab. As stated above, the loss of LN2 when filling Dewars using traditional means results in an accelerated consumption of purchased liquefied gas. Working environments, such as lab size, often result in multiple Dewars operating in more than one area at any given time. Further, each Dewar requires individual servicing and monitoring.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present application, there is a need in the art for an improved method for filling a liquefied gas container.
Embodiments of the present invention address problems with gas metering and containment and will be understood by reading and studying the following specification. In one embodiment, a method for filling a pressurized container is provided. The method involves automatically adjusting a shutoff valve between a supply of a pressurized medium and the pressurized container based on a weight of the pressurized medium contained in the pressurized container.
In another embodiment, an apparatus for metering a supply of liquefied gas to a liquefied gas container is provided. The apparatus includes means for determining a current weight of the liquefied gas container and means, associated with the means for determining, for allowing liquefied gas to enter the liquefied gas container The apparatus further includes means, associated with the means for determining and the means for allowing, for indicating a current level of liquefied gas contained in the liquefied gas container.
In yet another embodiment, a liquefied gas containment system is provided. The system includes a Dewar tank mounted on a scale and seated within a mobile base, an intake and relief valve assembly mounted on top of the Dewar tank and coupled to a main fill line, a shutoff valve coupled between the main fill line and a removable feed line, and a scale linkage connecting the scale and the shutoff valve. The system further includes wherein the scale linkage adjusts one or more positions of the shutoff valve based on an amount of the liquefied gas detected in the Dewar tank by the scale.
In still another embodiment, a method for maintaining a level of pressurized medium in a pressurized container is provided. The method involves establishing a starting level reading by indicating with a level readout that the pressurized container does not contain a substantial amount of the pressurized medium. As the pressurized medium enters the pressurized container, the method involves adjusting a shutoff valve as an increase in weight of the pressurized container is detected. As the weight of the pressurized container increases, the method further involves adjusting a current level reading on the level readout. Once the pressurized container is substantially filled with the pressurized medium, the method still further involves automatically closing the shutoff valve. The method concludes as the pressurized medium is removed from the pressurized container, and the level readout is updated to indicate an adjusted level based on a current weight of the pressurized container.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.
Embodiments of the present invention address problems with filling a liquefied gas container. Particularly, in one embodiment, a method for filling a pressurized container is provided. The method involves automatically adjusting a shutoff valve between a supply of a pressurized medium and the pressurized container based on a weight of the pressurized medium contained in the pressurized container.
Although the examples of embodiments in this specification are described in terms of liquefied gas containment and metering, embodiments of the present invention are not limited to liquefied gas containment and metering. Embodiments of the present invention are applicable to any gas containment and metering activity that requires continuous knowledge of an amount of a gaseous element filling a container, and automatically discontinuing a filling of the gaseous element into the container once a desired level is reached. Alternate embodiments of the present invention utilize an automatic Dewar LN2 supply shutoff and metering system incorporating at least a scale and a shutoff valve linked together. The system is adapted for use with Dewars of different capacities. In addition, a gauge mechanism accurately records a remaining level of LN2 in the Dewar at all times. Moreover, the entire system is suited for placement on a mobile base.
In one embodiment, Dewar tank 102 is secured on scale 106 by at least one tank latch 116. Moreover, the at least one tank latch 116 is mechanically mounted on top of scale 106. Scale 106 is seated within mobile base 104 with scale seat mounts 1071 to 1074. In one embodiment, mobile base 104 is constructed with raised sides to prevent a combination of Dewar tank 102 and scale 106 from sliding off. It is noted that for simplicity in description, scale seat mounts 1071 and 1074 are shown in
Scale 106 further includes adjustment knob 114 and scale linkage 134. Adjustment knob 114 is used to tare, or determine a weight of, an empty Dewar tank 102. The tare value of the empty Dewar tank 102 is used in the operation of system 100, as further described below. Including adjustment knob 114 allows the use of one or more Dewar tanks with varying dimensions, e.g. of one or more tare values. In one embodiment, scale linkage 134 provides a mechanical link between scale 106 and shutoff valve 120. Moreover, scale linkage 134 places shutoff valve 120 in an open position once scale 106 is tared for the weight of the empty Dewar tank 102. In another embodiment, scale linkage 134 is mechanically coupled to level gauge link 136. Moreover, level gauge link 136 provides an analog measurement to level gauge 118. The operation of level gauge 118 is further described below.
Prior to operation, adjustment knob 114 is adjusted until a starting reading of scale 106 is substantially equal to the weight of Dewar tank 102 when Dewar tank 102 does not contain a substantial amount of liquefied gas. In one embodiment, once the starting reading of scale 106 is established, scale linkage 134 is adjusted to an initial starting position so that a final reading of scale 106, e.g., a reading of scale 106 when Dewar tank 102 is filled with liquefied gas, will position shutoff valve 120 in a closed position. Moreover, current valve positions of shutoff valve 120 will be maintained by current positions of scale linkage 134. Scale linkage 134 is adjusted to position shutoff valve 120 in a fully-open position prior to operation. In one embodiment, once scale linkage 134 is adjusted, feed line 112 is attached to shutoff valve 120 with shutoff valve inlet coupler 122. Next, a liquefied gas is supplied to system 100 by feed line 112. As the liquefied gas enters system 100, the liquefied gas is transported through main fill line 126 and overhead fill line 128. Eventually, the liquefied gas enters Dewar tank 102 through intake and relief valve assembly 132. As the liquefied gas begins to fill Dewar tank 102, scale 106 begins to detect an increase in weight of Dewar tank 102. In one embodiment, the increased weight of Dewar tank 102 causes scale 106 to automatically adjust a current position of scale linkage 134. An adjusted position of scale linkage 134 begins closing shutoff valve 120. In one embodiment, the adjusted position of scale linkage 134 adjusts a current position of level gauge link 136. Moreover, an adjusted position of level gauge link 136 changes a current reading of level gauge 118. In the case of an increase in weight of Dewar tank 102, the current reading of level gauge 118 indicates an increase in the amount of liquefied gas, i.e. a current level, present in Dewar tank 102.
As additional liquefied gas enters system 100, scale linkage 134 is continually repositioned, adjusting shutoff valve 120 closer to the closed position. At a time when scale 106 detects that Dewar tank 102 is substantially filled with the liquefied gas, scale linkage 134 is in a final position and places shutoff valve 120 in the closed position. Once shutoff valve 120 is in the closed position, shutoff valve 120 is prevented from automatically re-opening. In one embodiment, the final position of scale linkage 134 adjusts level gauge link 136 to change the current reading of level gauge 118 to indicate that Dewar tank 102 is filled with the liquefied gas. Moreover, level gauge link 136 and scale linkage 134 remain in operation once system 100 is disconnected from feed line 112. Further, level gauge 118 continues to provide an indication of the current level of liquefied gas remaining in Dewar tank 102. In one embodiment, once Dewar tank 102 is filled, feed line 112 is removed from system 100. System 100 is capable of being transported via mobile base 104. As the liquefied gas is used, scale 106 will record a decrease in weight of Dewar tank 102. In response, level gauge link 136 adjusts the current reading of level gauge 118. Level gauge 118 will indicate a decrease in the amount of liquefied gas present in Dewar tank 102.
Filling a Dewar tank with liquefied gas using the automated shutoff and metering mechanism described above eliminates a need for constant manual monitoring of a fill operation. The fill operation is started and proceeds without additional intervention required. The amount of liquefied gas used to fill the Dewar tank is never over-exceeded. Further, the addition of a level gauge near the bottom of the Dewar tank provides constant indication of the amount of liquefied gas remaining in the Dewar tank. The placement of the level gauge near the bottom of the tank eliminates difficulties in reading the gauge under conditions of frost accumulation on the top of the Dewar tank.
In operation similar to that described with respect to
As additional liquefied gas enters system 200, valve control interface 204 continually adjusts shutoff valve 120 closer to the closed position. At the time when scale 106 detects that Dewar tank 102 is filled with the liquefied gas, valve control interface 204 has placed shutoff valve 120 in the closed position. Once shutoff valve 120 is placed in the fully closed position, valve control interface 204 will no longer change the valve position of shutoff valve 120. In one embodiment, the closed position of shutoff valve 120 translates to the current reading of level meter 208 to indicate that Dewar tank 102 is filled with the liquefied gas. Moreover, control unit 202 remains in operation once system 100 is disconnected from feed line 112. Further, level meter 208 continues to provide an electronic indication, e.g., digital readout, of the amount of liquefied gas remaining in Dewar tank 102. Similar to the embodiment described above with respect to
At block 302, the method begins by establishing a starting reading on a scale with a scale linkage before proceeding to block 304. In one embodiment, establishing the starting reading on the scale further includes adjusting the scale until the starting reading is substantially equal to a weight of the container when the container does not contain a substantial amount of gas.
At block 304, the method continues by adjusting the scale linkage to an initial starting position to place a shutoff valve, attached to the liquefied gas container, in a fully open position before proceeding to block 306. In one embodiment, adjusting the scale linkage further includes adjusting for a final reading that will place the shutoff valve in a closed position. Moreover, the final reading corresponds to a reading of the scale when the container is filled with the liquefied gas.
At block 306, the method attaches a gas feed line to the shutoff valve before proceeding to block 308. At block 308, as liquefied gas enters the container, the method detects an increase in weight of the container. As the weight of the container increases, adjusting a current position of the scale linkage is adjusted at block 310. In one embodiment, the current position of the shutoff valve is maintained by a current position of the scale linkage. At block 312, the method concludes by positioning the shutoff valve in a fully closed position and the scale linkage in a final position once the scale detects that the container is substantially filled with the liquefied gas. In one embodiment, the scale linkage is prevented from automatically re-opening the shutoff valve once the shutoff valve is in the fully closed position.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the following claims and the equivalents thereof.
