1. Field of the Invention
This invention relates generally to storage and dispensing systems for the selective dispensing of fluids from a vessel in which the fluid component(s) are sorptively retained by a solid sorbent medium, and are desorptively released from the sorbent medium in the dispensing operation. More particularly, the present invention relates to a method and apparatus for determining internal pressure and temperature in the vessel of the storage and dispensing system, in situ.
2. Description of the Related Art
In a wide variety of industrial processes and applications, there is a need for a reliable source of process fluid(s) which is compact, portable, and available to supply the fluid(s) on demand. Such processes and applications include semiconductor manufacturing, ion implantation, manufacture of flat panel displays, medical treatment, water treatment, emergency breathing equipment, welding operations, space-based applications involving delivery of liquids and gases, etc.
U.S. Pat. No. 4,744,221 issued May 17, 1988 to Karl O. Knollmueller discloses a method of storing and subsequently delivering arsine, by contacting arsine at a temperature of from about -30.degree. C. to about +30.degree. C. with a zeolite of pore size in the range of from about 5 to about 15 Angstroms to adsorb arsine on the zeolite, and then dispensing the arsine by heating the zeolite to an elevated temperature of up to about 175.degree. C. for sufficient time to release the arsine from the zeolite material.
The method disclosed in the Knollmueller patent is disadvantageous in that it requires the provision of heating means for the zeolite material, which must be constructed and arranged to heat the zeolite to sufficient temperature to desorb the previously sorbed arsine from the zeolite in the desired quantity.
The use of a heating jacket or other means exterior to the vessel holding the arsine-bearing zeolite is problematic in that the vessel typically has a significant heat capacity, and therefore introduces a significant lag time to the dispensing operation. Further, heating of arsine causes it to decompose, resulting in the formation of hydrogen gas, which introduces an explosive hazard into the process system. Additionally, such thermally-mediated decomposition of arsine effects substantial increase in gas pressure in the process system, which may be extremely disadvantageous from the standpoint of system life and operating efficiency.
The provision of interiorly disposed heating coil or other heating elements in the zeolite bed itself is problematic since it is difficult with such means to uniformly heat the zeolite bed to achieve the desired uniformity of arsine gas release.
The use of heated carrier gas streams passed through the bed of zeolite in its containment vessel may overcome the foregoing deficiencies, but the temperatures necessary to achieve the heated carrier gas desorption of arsine may be undesirably high or otherwise unsuitable for the end use of the arsine gas, so that cooling or other treatment is required to condition the dispensed gas for ultimate use.
U.S. Pat. No. 5,518,528 issued May 21, 1996 in the names of Glenn M. Tom and James V. McManus, describes a gas storage and dispensing system, for the storage and dispensing of gases, e.g., hydride gases, halide gases, organometallic Group V compounds, etc. which overcomes various disadvantages of the gas supply process disclosed in the Knollmueller patent.
The gas storage and dispensing system of the Tom et al. patent comprises an adsorption-desorption apparatus, for storage and dispensing of gases, including a storage and dispensing vessel holding a solid-phase physical sorbent, and arranged for selectively flowing gas into and out of the vessel. A sorbate gas is physically adsorbed on the sorbent. A dispensing assembly is coupled in gas flow communication with the storage and dispensing vessel, and provides, exteriorly of the vessel, a pressure below the vessel's interior pressure, to effect desorption of sorbate from the solid-phase physical sorbent medium, and flow of desorbed gas through the dispensing assembly. Heating means may be employed to augment the desorption process, but as mentioned above, heating entails various disadvantages for the sorption/desorption system, and it therefore is preferred to operate the Tom et al. system with the desorption being carried out at least partially by pressure differential-mediated release of the sorbate gas from the sorbent medium.
The storage and dispensing vessel of the Tom et al. patent embodies a substantial advance in the art, relative to the prior art use of high pressure gas cylinders. Conventional high pressure gas cylinders are susceptible to leakage from damaged or malfunctioning regulator assemblies, as well as to rupture and unwanted bulk release of gas from the cylinder if the internal gas pressure in the cylinder exceeds permissible limits. Such overpressure may for example derive from internal decomposition of the gas leading to rapid increasing interior gas pressure in the cylinder.
The gas storage and dispensing vessel of the Tom et al. patent thus reduces the pressure of stored sorbate gases by reversibly adsorbing them onto a carrier sorbent, e.g., a zeolite or activated carbon material.
The storage and dispensing system broadly described above is usefully employed for safe storage and dispensing of toxic and hazardous gases, as well as other sorbable fluids. Such storage and dispensing system permits sub-atmospheric pressure storage and use of a wide variety of sorbable fluids which are sorbable onto an appropriate microporous sorbent medium.
The storage and dispensing vessel used in such system may comprise an ordinary high pressure cylinder of the type used to store gases at super-atmospheric pressure levels, but containing a suitable sorbent medium on which the sorbable fluid is stored or adsorbed.
A manual or automated (by electrical or air means) high pressure stainless steel diaphragm valve typically is employed to ensure containment of the sorbable fluid within the storage and dispensing vessel. Under normal conditions, the internal cylinder pressure and temperature are effectively maintained within desired limits, including a pressure level less than 1 atmosphere and a temperature on the order of 25.degree. C. or less. These conditions of pressure and temperature preclude pressure-mediated release, which is a significant risk in conventional practice where cylinders are filled with super-atmospheric pressure gas, and the danger of rupture or leakage is exacerbated by the high pressures involved.
Despite the foregoing advantages of low pressure operation with the aforementioned sorbent-based storage and dispensing system, such storage and dispensing systems during storage and transportation may be exposed to heat or warming conditions which correspondingly warm the sorbent material in the cylinder and result in cylinder pressure increasing to levels in excess of 1 atmosphere.
In use of such sorbent-based storage and dispensing systems, utilizing sorbent media such as zeolite compositions, activated carbon and the like, it has been found that the pressure dependence on temperature in the cylinder is on the order of from 0.5 psi/.degree.C. to 0.75 psi/.degree.C.
In view of such temperature/pressure fluctuations in the storage and transport of the sorbent-based storage and dispensing system, it would be a significant advance in the art to provide a means and method of monitoring the pressure and temperature in the sorbable fluid storage and dispensing vessel of such systems, so that appropriate safety and handling procedures can be utilized, when temperature and/or pressure in the sorbent-containing vessel exceed normal desired operating values.
It is an object of the invention to provide such means and method.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure.
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