Refrigeration – Storage of solidified or liquified gas – With vapor discharged from storage receptacle
Reexamination Certificate
2001-10-15
2003-01-14
Doerrler, William C. (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
With vapor discharged from storage receptacle
Reexamination Certificate
active
06505469
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to systems for dispensing cryogenic gases from vessels storing cryogenic liquids and, more particularly, to a dispensing system for cryogenic liquid vessels that provides cryogenic gas at high pressures and high flow rates.
Cryogenic gases are used in a variety of industrial and medical applications. Many of these applications require that the cryogen be supplied as a high pressure gas. For example, high pressure nitrogen and argon gases are required for laser welding while high pressure nitrogen, oxygen and argon gases are required for laser cutting. Such cryogens are typically stored as liquids in vessels, however, because one volume of liquid produces many volumes of gas (600-900 volumes of gas per one volume of liquid) when the liquid is permitted to vaporize/boil and warm to ambient temperature. To store an equivalent amount of gas requires that the gas be stored at very high pressure. This would require heavier and larger tanks and expensive pumps or compressors.
Cryogenic vessels typically consist of an insulated double-walled tank for storing cryogenic liquids. It is impossible, however, to prevent all heat transfer between the interior of the tank and the external environment. As a result, the cryogenic liquid in the tank will slowly expand, and eventually vaporize, so as to pressurize the tank. Cryogenic gas will collect in the head space of the tank. Because the cryogen is used as a gas, it is advantageous to use the gas in the head space before vaporizing the liquid within the tank. Using gas from the head space reduces pressure in the head space so that venting may be avoided.
A disadvantage with supplying cryogenic gas from the head space of the tank is that the head space pressure will not always be sufficient to meet the use requirements. When the head space pressure is insufficient, the liquid in the tank must be vaporized to meet the use requirements and rebuild the head space pressure.
A prior art dispensing system that coordinates the supply of cryogenic gas from the head space and liquid body of a tank is illustrated in FIG.
1
. Such a system is available from Chart Inc. of Burnsville, Minn., owner of the present application. As illustrated in
FIG. 1
, the system includes a cryogenic liquid storage vessel, indicated in general at
6
, including an inner tank
8
and a jacket
10
. The inner tank
8
holds a supply of cryogenic liquid, shown at
12
. The head space
14
of the inner tank contains cryogenic gas that forms due to the transfer of heat between the interior of the inner tank of the vessel and the external environment.
To further pressurize the vessel, a pressure builder coil
16
is connected to the bottom of inner tank
8
via liquid feed and trap
17
and helically disposed around inner tank
8
and in contact with jacket
10
. The cryogenic liquid is free to flow from the inner tank into coil
16
. Because pressure building coil
16
is in contact with the jacket
10
of the vessel, heat transfer between the external environment and the liquid in coil
16
will be relatively great. As a result, the cryogenic liquid in the coil will be vaporized. Coil
16
is connected to pressure building line
18
which communicates with the head space
14
of vessel
6
via a circuit
19
that includes a pressure building valve
20
and a pressure building regulator
22
(preferably a diaphragm regulator) and a return line
24
.
In addition, return line
24
connects the head space
14
of vessel
6
to a by-pass line
26
containing an economizer regulator
28
. By-pass line
26
and regulator
28
connects circuit
19
and return line
24
to a vaporizer line
29
and a vaporizer
30
that is connected to a gas use line
32
. Like coil
16
, vaporizer
30
is helically disposed about the inner tank
8
and connected to the jacket
10
of vessel
6
such that heat transfer to vaporizer
30
will be great enough to vaporize any cryogenic liquid therein before it is delivered to gas use line
32
. Gas use line
32
includes a gas use valve
34
for controlling the delivery of gas for its intended use. A dip tube
36
having a lower end positioned within the cryogenic liquid
12
also communicates with vaporizer line
29
, and thus, vaporizer
30
and gas use line
32
.
Economizer regulator
28
is set to close when the pressure within the head space
14
of the vessel
6
drops below a first predetermined level. Pressure building regulator
22
is set to open when the pressure within the head space drops below a second predetermined level that is lower than the first predetermined level at which the economizer regulator
28
is set to close. As such, pressure building and economizer regulators
22
and
28
, respectively, are never open simultaneously.
To dispense cryogenic gas, gas use valve
34
is opened. When the pressure within the head space
14
of vessel
6
is above the pressure setting of economizer
28
, so that economizer
28
is open, gas travels from the head space
14
of the vessel
6
through return line
24
, by-pass line
26
, vaporizer line
29
, vaporizer
30
and ultimately to gas use line
32
.
If the pressure of head space
14
falls below the first predetermined value set at economizer regulator
28
, economizer
28
will close. Under such circumstances, when gas use valve
34
is open, cryogenic liquid is withdrawn from the inner tank
8
via dip tube
36
and directed to vaporizer coil
30
. The liquid is converted to gaseous cryogen in the vaporizer coil and is delivered to valve
34
via use line
32
.
If the pressure of head space
14
falls below the second predetermined value set at pressure building regulator
22
, regulator
22
opens and, if pressure building valve
20
is open, liquid is removed from the bottom of inner tank
8
via feed
17
and enters pressure building coil
16
where it is vaporized and delivered to pressure building line
18
. The resulting gas will flow through circuit
19
and, because economizer regulator
28
is closed, through return line
24
so that the head space
14
is pressurized.
Industrial applications such as laser welding and cutting require that the cryogenic gases be provided simultaneously at high pressures and flow rates. Advances in industrial laser technologies have resulting in demands for increased flow rates. Pressures in the range of approximately 400-420 psig and flow rates in the range of approximately 1500-2500 scfh are now typical. While the system described above is effective at dispensing gases at such pressure levels, and indeed up to around 500 psig, it encounters difficulties in maintaining these operating pressures at such high flow rates.
Accordingly, it is an object of the present invention to provide a gas dispensing system for cryogenic liquid vessels that is capable of delivering high pressure gas at high flow rates.
It is another object of the present invention is to provide a gas dispensing system for cryogenic liquid vessels that may be retrofitted to earlier cryogenic liquid vessels and gas dispensing systems.
It is another object of the present invention to provide a gas dispensing system for cryogenic liquid vessels that is economical to operate.
It is still another object of the present invention to provide a gas dispensing system for cryogenic liquid vessels that is inexpensive to produce and maintain.
Other objects and advantages will be apparent from the remaining portion of this specification.
SUMMARY OF THE INVENTION
The present invention is directed to a system for dispensing pressurized cryogenic gas at high flow rates. The system includes a storage vessel having a jacket surrounding an inner tank that contains a supply of cryogenic liquid with a head space there above. An internal pressure builder coil is positioned between the jacket and inner tank, is in contact with the jacket and is helically positioned about the inner tank. An external pressure building heat exchanger is in communication with the internal pressure builder and the head space of the inner tank of the storage
Drube Paul
Sjogren Paul
Chart Inc.
Doerrler William C.
Drake Malik N.
Piper Rudnick
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