Helical built-in purifier for gas supply cylinders

#Industrial gases which are utilized in small to moderate volumes are stored at ambient temperature in pressurized cylinders from which gas is withdrawn as needed. Gases which have critical temperatures below ambient temperature are stored at high pressures determined by the design pressure ratings of the cylinders. Examples of these include low-boiling gases such as nitrogen, oxygen, hydrogen, helium, and methane, which are withdrawn from the storage cylinders without phase change. Gases which have critical temperatures above ambient temperature are stored in cylinders as saturated liquids at their respective vapor pressures, and these liquids vaporize as saturated vapor which is withdrawn from the cylinders. Common examples of such liquefied compressed gases are chlorine, ammonia, and light hydrocarbons such as propane and butane.

#There is a need in certain industries for very high purity gases supplied by cylinders as described above. For example, very high purity gases are utilized in the electronics industry for manufacturing semiconductor and optoelectronic devices, video display panels, fiber optic devices, and micro-electromechanical systems. Examples of such gases include hydrogen chloride, hydrogen bromide, hydrogen fluoride, chlorine, ammonia, tungsten hexafluoride, disilane, dichlorosilane, trimethylsilane, and boron trichloride.

#The demand for higher purity levels of these gases, especially those supplied as liquefied compressed gases, is growing and there is a trend towards processes which consume these gases at higher flow rates. This trend toward higher usage rates is driven in part by the larger size of the substrate materials used in the manufacturing processes mentioned above. These higher flow rates, in turn, have generated a demand for larger sizes of transportable cylinders used to deliver these high purity gases. Such larger cylinders can provide these higher flow rates while reducing the frequency of cylinder return to the gas suppliers for refilling.

#FIG. 1 shows an embodiment of the present invention having a helical purifier tube assembly disposed in a portion of the interior length of a single-ended fluid cylinder.

#FIG. 2 is an enlarged view of a section of FIG. 1.

#FIG. 3 shows another embodiment of the invention having a helical purifier tube assembly disposed in the entire interior length of a single-ended fluid cylinder.

#High purity gases can be supplied to end users from pressurized cylinders containing a single gas phase or coexisting liquid and vapor phases. In the first of these supply modes, the gas pressure in the cylinder drops as gas is withdrawn, and gas pressure to the consumer is controlled by a pressure regulator. In the second of these supply modes, a compressed liquefied gas is stored in the cylinder and vapor is withdrawn therefrom while the liquid vaporizes; the cylinder pressure is the existing vapor pressure. Gas pressure to the consumer is controlled at a pressure below the vapor pressure by a pressure regulator.

#Undesirable impurities may be present in the fluid stored in the cylinder and these impurities can be removed readily by means of a built-in purifier located inside of the cylinder. These impurities may include undesirable soluble compounds such as water, carbon dioxide, hydrocarbons, metal salts, and oxygen, and also may include insoluble particulate material. The purifier may be a cylindrical vessel or tube which contains one or more materials selected from adsorbents, catalysts, and getters which are capable of removing the soluble impurities to very low concentration levels, typically down to levels of parts per billion by volume (ppbv). The purifier also may include a filter to remove particulate material. In prior art applications of built-in purifiers, the purifier assembly typically is attached to the cylinder valve inlet port and is designed to fit through the cylinder neck.

#The purifier assembly initially is charged with the purification materials, attached to the inlet of the valve, the purifier assembly is inserted through the cylinder neck, and the valve (which has a threaded inlet section) is screwed into the threads in the cylinder neck to seal the purifier into the cylinder. The cylinder is filled with the product fluid (gas or liquid). Gas then is withdrawn through the purifier, impurities are removed therein, and a high-purity gas product is withdrawn through the valve to the consumer. When the purification materials become spent after a period of operation, the valve is unscrewed from the cylinder, the spent purification materials are replaced or regenerated, and the purifier and valve are reinstalled in the cylinder.