Patent Application
20080271466
None
Liquified gases that are normally stored, or initially produced, in the liquid state at low or very low temperatures often need to be purified to an acceptable level of purity associated with their end use. It would be advantageous if they could be purified easily and economically. The term, liquified gas, is defined as a substance in a liquid state that otherwise predominantly exist as a gas if it is maintained at one atmosphere and 15° C. A few specific examples of such include Nitrogen, Oxygen, Helium, Neon, Argon, Krypton Xenon, Hydrogen, Methane, and Carbon Dioxide.
A first method is disclosed for providing a purified liquified gas that includes the following steps:
A second method is disclosed for providing a purified liquified gas including the following steps:
A system is disclosed for providing a purified liquified gas that includes the following elements:
The first method or second method or system can also include one or more of the following aspects:
For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawing, and wherein:
The Figure is a schematic of a particular embodiment of the disclosure.
This invention concerns the purification of liquified gases that are normally stored, or initially produced, in the liquid state at low or very low temperatures. The purification apparatus that can be used to remove dissolved or entrained impurities within the initially produced (and nearly pure) liquified gas includes one or more vessels containing a suitable pre-activated adsorbent material such as a molecular sieve, activated carbon, silica gel, activated alumina, or an inert material impregnated with metals or metal alloys (such as Pd/Al2O3 or Hopcalite), and the like.
The vessel containing adsorbent is submerged within the liquified gas to be purified contained in a storage tank. Thus, cooling of the vessel may be achieved by direct contact with the liquified gas to be purified or by exchanging heat between the liquified gas and the vessel via a heat exchange fluid. Optionally, the vessel may be vacuum-jacketed. Preferably, the vessel will be installed near or at the bottom of the storage tank in which they are to be used.
The purification process involves passing the liquified gas through at least one (the first) vessel containing adsorbent and then allowing the purified liquified gas to exit the vessel and then exit the storage tank into a piping system leading to either a different storage tank, conventional external vaporizers (if the gas phase of the purified liquid must be produced) or to a point of use if it is to be used directly in the liquid state. Following the external vaporization process, the purified gas may be directed through an appropriate piping network to a point of use location.
The vessel may have filters at one or both ends to provide pre-filtration of solid particles entrained in the liquified gas and/or post-filtration of solid particles in the purified liquified gas that may be caused by dislodgement of the adsorbent.
External low temperature or cryogenic valves (either manually automatically controlled) attached by an appropriate piping network can be used to control the flow of the liquified gas to be purified through the vessel or to bypass the vessel, if necessary, or to redirect the flow of liquified gas through additional vessels containing adsorbent.
Conventional analytical techniques can be used to monitor the concentration of impurities within the purified liquified gas in order to monitor the performance of a particular adsorbent vessel in current use. If and when a selected impurity breakthrough occurs, the liquified gas to be purified can be directed (either manually or automatically) into a second vessel containing adsorbent and the purification process can be resumed as noted above.
Regeneration of the vessel can be achieved without heating by allowing the entire empty bulk storage tank (as well as the vessel) to warm up to ambient temperatures while, at the same time, venting the vaporized contents of the vessel to the ambient atmosphere. This process will allow the desorption of practically all adsorbed impurities trapped within the adsorbent.
Alternatively, a more rapid and complete regeneration process can be achieved by passing an ambient temperature (or heated) flow of a purge gas through a vessel containing spent adsorbent. The purge gas can be a gaseous form of the same liquified gas initially purified or it may be another less expensive gas. For example, if liquid Helium had been initially purified in this way, a cheaper purge gas (such as Nitrogen or Argon) might be used during the purging/regeneration process since these gases are much less expensive than relatively pure Helium. All of the above noted manipulations can be preformed manually or automatically through externally located manual or automatic valves.
In addition to the above noted operation, the vessel containing adsorbent may be designed to contain a vacuum jacketed covering that would facilitate the installation of an electrical heating system inside the vessel so it could be regenerated by internal heating as well as using an external flow of some type of purge gas during the heating process. This kind of regeneration process could be executed even if the bulk fluid storage tank was not empty.
A further improvement associated with this purification process is that it allows for the purification of very cold liquified gases even if they exist at temperatures well above their normal boiling points and well above 1.0 atmosphere in pressure while still existing in the liquid state within a suitable high pressure storage tank. Two typical examples of these kinds of fluids are liquid Nitrogen and liquid Oxygen stored within conventional high-pressure bulk cryogenic storage tanks.
In the case of standard bulk liquid Nitrogen storage tanks, the ullage pressure may typically be deliberately set at about 90 psig (low pressure source) to about 160 psig (high pressure source), depending on a particular user's requirements. These pressures may be achieved within the bulk liquid storage tanks by allowing the liquid Nitrogen to reach temperatures that maintain a preset value for the stored liquid's temperature. These temperatures may be reached via ambient temperature heat leaks through the storage tank walls into the fluid to be purified or by using some other type of active heat exchanger well known to those skilled in the art, for example, a pressure building coil located outside of the bulk fluid storage tank.
In the case of liquid Nitrogen at 90 and 160 psig, the temperatures that are associated with these liquid vapor pressures are about 99° K and 106° K, respectively. These temperatures are still very cold but they are also about 22° K and 29° K, respectively, hotter than the normal boiling point of liquid Nitrogen which is about 77° K (at 1.0 atmosphere absolute).
A typical storage tank pressure for bulk liquid oxygen is about 120 psig. At this pressure, the temperature of the self-pressurized liquid Oxygen is about 118° K. So, under these conditions, the liquid Oxygen is still very cold, but it is also about 28° K hotter than the normal boiling point of 90.2° K (at 1.0 atmosphere absolute) for liquid Oxygen.
1) storage vessel
2) pressurized, low temperature fluid to be purified
3) relief valve
4) adsorbent filled vessel
5) adsorbent filled vessel
6) adsorbent filled vessel
7) conduit
8) relief valve
9) fluid flow control valve to vaporizers
10) conduit
11) fluid control valve to conduit 7
12) fluid flow control valve to adsorbent filled vessel 4
13) fluid flow control valve to adsorbent filled vessel 5
14) conduit
15) conduit
16) conduit
17) conduit
18) conduit
24) fluid flow control valve to adsorbent filled vessel 6
As shown in the Figure, one particular embodiment includes three separate adsorbent vessels 4, 5, 6 installed inside of a conventional bulk storage tank 1 containing a liquified gas 2. During purification, liquified gas 2 exits the tank 1 via conduit 10. Valve 11 is closed thereby preventing delivery of the liquified gas without first being purified by the adsorbent filled vessels 4, 5, 6. One or more of valves 12, 13, 24 are open thereby allowing liquified gas 2 to flow into adsorbent filled vessels 4, 5, 6, respectively, via conduit 18. Much of the entrained or dissolved impurities in the liquified gas 2 is adsorbed by vessels 4, 5, 6. The thus-purified liquified gas 2 exits the adsorbent filled vessels 4, 5, 6 and enters conduit 7 via conduits 14, 15, 16, respectively. Valve 9 controls the flow of purified fluid 2 in conduit 7 to either external vaporizers (not shown), a different storage tank (not shown) or a point of use (not shown).
If for some reason, purification via the adsorbent filled vessels 4, 5, 6 is not desired but a flow of liquified gas 2 to the external vaporizers, different storage tank, or point of use is desired, valves 12, 13, 24 are closed and valve 11 is opened allowing the fluid 2 to directly enter conduit 7. Also, as apparent to one of ordinary skill in the art, one or more of the adsorbent filled vessels 4, 5, 6 may be isolated via manipulation of valves 12, 13, 24 thereby preventing purification of the fluid 2 by that adsorbent filled vessel or vessels 4, 5, 6. In this manner, purification of the liquified gas 2 may occur inside one or two of the vessels 4, 5, 6, while the adsorbent in two or one of the vessels 4, 5, 6 is regenerated.
All external piping lines (except for piping networks that are downstream of external vaporizers) are preferably vacuum insulated (or otherwise insulated) if used to convey low temperature fluids.
Additional valves may be used to direct selected external sources of a purge gas through the adsorbent filled vessels 4, 5, 6. In such case, one typical location is between valve 11 and valves 12, 13, 24. Venting valves may also be located between valve 9 and relief valve 8 to facilitate the regeneration process. Finally, pressure relief valves 3, 8 may be activated in case of too great a pressure is reached.
Preferred processes and apparatus for practicing the present invention have been described. It will be understood and readily apparent to the skilled artisan that many changes and modifications may be made to the above-described embodiments without departing from the spirit and the scope of the present invention. The foregoing is illustrative only and that other embodiments of the integrated processes and apparatus may be employed without departing from the true scope of the invention defined in the following claims.
