Oxygen Generator With Two Compressor Stages

The present invention pertains to the art of molecular separation, specifically the physical separation or fractionating of molecular components of a gaseous mixtures. The invention finds particular application in the separation of oxygen from the other components of atmospheric air to supply oxygen to welding equipment and will be described with particular reference thereto. It is to be appreciated, however, that the present invention is also applicable to the separation of other gaseous mixtures and is particularly applicable to applications in which the segregated gases are to be supplied at relatively high pressures.

Heretofore, components have been separated or fractionated from gaseous mixtures utilizing a method and apparatus generally as described in U.S. Pat. No. 2,944,627, issued July 12, 1960 to Charles W. Skarstrom. The Skarstrom system pressurized the gaseous mixture to be fractionated with a compressor or the like. A crossover valving assembly channelled the pressurized gaseous mixture alternately to first and second vessels containing a molecular separation material. The crossover valving assembly further connected the vessel which was not receiving the gaseous mixture with a waste gas or secondary product discharge port. The molecular separation material selectively adsorbed one or more components of the gas and passed one or more other components connoted as a primary product gas. The primary product gas which passed through the vessel was channelled in part to a primary product outlet and in part to the other vessel. The primary product gas portion channelled to the other vessel flushed the adsorbed or secondary product gases therefrom out the secondary product discharge port. Cyclically, the crossover valving assembly switched the connection of the vessels with the incoming gaseous mixture and the secondary product discharge port. This cyclic switching of the vessels provided a continuing, though cyclically surging, flow of the primary product gas. Because the flow rate of the primary product gas varied at different portions of the cyclic switching cycle, a surge tank was commonly connected with the outlet so that a relatively even product flow would be provided by the apparatus.

For welding and other industrial operations, oxygen is supplied at 45 psi or better. In order to maintain a 45 psi pressure in the surge tank and compensate for a pressure drop across the vessels, the input compressor was required to supply the gaseous mixture to the vessels at about 65 psi. To produce oxygen at an average rate of 10 cubic feet per hour required about a one horsepower compressor. Higher oxygen supply rates required correspondingly higher horsepower compressors.

One of the drawbacks of the prior art oxygen generators for supplying oxygen to welding equipment was the relatively large amount of electrical or other energy consumed by the compressor. Another drawback was that the amount and pressure of output oxygen varied or surged during the production system as the vessels were switched. Yet another drawback was that the compressor was required to supply gas at about 65 psi to maintain about 45 psi in the surge tank.

The present invention contemplates a new and improved gas fractioning apparatus and method which provides primary product more efficiently, at a higher pressure, and with less energy consumption.

In accordance with the present invention, there is provided an apparatus for fractioning components of a gaseous mixture. A first or input compressor means provides a supply of the mixture to be fractionated at a first relatively low pressure, e.g., 15-18 psi. A valving means alternately channels the gaseous mixture from the first compressor means to an input end of at least first and second beds. The beds each contain a physical separation medium which adsorbs at least one adsorbable component of the mixture and passes at least one substantially nonadsorbable component or primary product gas. The beds are connected at an output end thereof with a second or booster compressor means which boosts the pressure of the primary product gas from a second relatively low pressure, e.g., 2-6 psi, adjacent its inlet to a relatively high pressure, e.g., 65 psi.

In accordance with another aspect of the present invention, there is provided a method of fractioning components of a gaseous mixture. The gaseous mixture is supplied at a first relatively low pressure alternately to at least two beds containing a physical separation medium which adsorbs at least one adsorbable component and passes at least one substantially nonadsorbable component or primary product gas. The pressure of the primary product gas downstream from the beds is maintained at a second relatively low pressure, e.g., 2-6 psi, and boosted to a relatively high pressure, e.g., 65 psi, at a primary product gas outlet.

One advantage of the present invention is that it produces the primary product gas more efficiently. Particularly, the back pressure at the primary product outlet end of the beds is maintained relatively low and relatively constant. This produces a relatively flat output flow rate of the primary product gas from the beds which, in turn, produces more useable product.

Another advantage of the present invention is that it provides a substantial power savings. The total horsepower consumed by the two compressors is about half the horsepower required by the input compressors of the prior art. For example, a one-third horsepower input compressor and a one-fifth horsepower booster compressor have been found to produce about 81/2 cubic feet per hour. As is to be appreciated, this is about half the one horsepower required in the above-described prior art apparatus to produce ten cubic feet per hour of comparably pure oxygen.

Another advantage of the present invention is that it enables larger amounts of oxygen to be stored. The present invention enables oxygen to be stored at 65 psi or even 100 psi or more. Under these higher pressures substantially more oxygen can be stored in the same size storage tank than at the 45 psi as commonly stored prior art units.

Still further advantages of the present invention will become apparent upon reading and understanding the following detailed description of the preferred embodiment.

The invention may take form in various steps and arrangements of steps and in various parts and arrangements of parts. The drawings are only for purposes of illustrating a preferred embodiment to the invention and are not to be construed as limiting it.

FIG. 1 is a block diagram of an apparatus in accordance with the present invention for separating a primary product gas from a gaseous mixture; and,

FIG. 2 is a diagrammatic illustration of an electrical control circuit for the apparatus of FIG. 1.

With reference to FIG. 1, a first or input compressor means A supplies a gaseous mixture, such as atmospheric air, at a first relatively low pressure, to a molecular sieve bed assembly B. The molecular sieve bed assembly separates a primary product gas, such as oxygen, from the gaseous maixture. A second or boster compressor means C draws the primary product gas from the molecular sieve bed assembly B and boosts its pressure to a relatively high pressure. The relatively high pressure primary product gas is supplied to a primary product outlet which is adapted to be interconnected with welding equipment D or the like. A flow and pressure regulating means E regulates the flow rate and pressure of the primary product gas between the molecular sieve bed assembly and the booster compressor means to maintain optimum primary product production conditions. By adjusting the pressure and flow rates, the production rate and the purity of the primary product are selectively adjustable. A control circuit F controls the operation and cycling of the first compressor means, the molecular sieve bed assembly, the second compressor means, and other components.

The first compressor means A includes a compressor, such as a carbon vane compressor, 10 which compresses atmospheric air or another received gaseous mixture to a first relatively low pressure, in the preferred embodiment, about 15-18 psi. However, other pressures below 45 psi are also contemplated. A check valve 12 assures a unidirectional gaseous mixture flow from the first compressor 10 to a filter 14. The filter removes contaminants such as carbon dust, oil vapors, and the like from the gaseous mixture. A heat exchanger 16 conserves energy by cooling the gaseous mixture with a waste or secondary product gas as it expands into the atmosphere.

The molecular sieve bed assembly B includes a crossover valving means 20 which alternately directs the pressurized gaseous mixture to a first bed 22 and a second bed 24, while connecting the bed which is not receiving the gaseous mixture to a waste gas outlet port 26. In the preferred embodiment, the beds are filled with a physical separation medium or material which selectively adsorbs one or more adsorbable components or secondary product gases and passes one or more nonadsorbable components or primary product gases of the gaseous mixture. The physical separation material is a molecular sieve with pores of uniform size and essentially the same molecular dimensions. These pores selectively adsorb molecules in accordance with molecular shape, polarity, degree of saturation, and the like. In the preferred embodiment, the physical separation material is a zeolite which has pores of the appropriate dimension to adsorb nitrogen, carbon monoxide, carbon dioxide, water vapor, and other significant component of air, but not oxygen which is passed as the primary product gas rather than being adsorbed. Type 5A and type 13X zeolite have been found satisfactory.

The crossover valving means 20 under the control of the control circuit F alternates cyclically between a first position and a second position. In the first position, the gaseous mixture is channelled into the first bed first end. Primary product gas is discharged from the first bed second end through a first restrictor means 28. A portion of the primary product gas is channelled through a second restrictor means 30 into the second bed second end. The adsorbed secondary product gases are flushed from the second bed first end, through the crossover valve 20, and out the waste gas outlet port 26. Another portion of the primary product gas is channelled through a third restrictor means 32.

In the second crossover valve position, the gaseous mixture is channelled to the second bed first end. Primary product gas is discharged from the second bed second end through the second restrictor means 30. A portion of the primary product gas is channelled through the first restrictor means 28 to flush the adsorbed second product gases from the first bed. Another portion of the primary product gas is discharged through the third restrictor means 32.

The third restrictor means 32 is connected with the primary product output of the molecular sieve bed assembly B. The restrictiveness of the third restrictor means 32 relative to the first and second restrictor means 28, 30 determines the relative portion of the primary product gas which is returned to flush the bed being regenerated. A check valve 34 assures that the primary product gas is only discharged from the molecular sieve bed assembly B and that atmospheric air or other gases are not drawn in.

The pressure booster means C includes a second compressor means 40 such as a diaphragm type compressor. It is contemplated, that other types of compressors which are suitable for pumping and compressing about 95 percent pure oxygen gas may also be utilized. Compressor start up valving means 42, 44 enable the second compressor means 40 to be started free of load. After the second compressor means is started, the start up valving means are actuated to the position shown in FIG. 1 such that a primary product gas is drawn from the molecular sieve bed assembly B and supplied to a storage tank 46 at a relatively high pressure, 45 psi or more with 65 psi or more being preferred. However, it is contemplated that primary product gas may be stored at a lower pressure if the downstream equipment D can be operated at such lower pressures. As described in greater detail in conjunction with FIG. 2, a pressure sensing switch means 48 selectively actuates and deactuates the second compressor means 40 in order to maintain a preselected storage pressure in the storage tank 46. A check valve 50 assures that the primary product gas is received by the storage tank 46 but not discharged therefrom through the compressor start up valving means 42. An on-off primary product control switch 52 selectively enables and disables primary product gas to flow from the storage tank 46 to a primary product outlet 54. A check valve 56 assures that propane, acetylene, or other welding gases are not allowed to enter the primary product storage tank 46.

The flow and pressure control means E prevents the second compressor means 40 from drawing a vacuum on the first and second sieve beds. The second vacuum pump maintains relatively low, positive pressure at the primary product output end of the sieve beds. In the preferred embodiment, the pressure at the primary product output end of the beds is several pounds lower than the pressure supplied to the inlet end. This pressure differential reduces the amount of work required of the first compressor to move or pump the gas through the molecular sieve beds. Thus, the present invention permits the first compressor to have a lower horsepower because the sieve beds operate at a lower pressure.

The flow and pressure regulating means E include a fourth restrictor 60 to reduce the output pressure of the sieve bed assembly B still further. The fourth restrictor smooths the primary product flow rate and pressure from the sieve bed assembly sufficiently that no surge tank is required. In the preferred embodiment, the fourth restrictor means 60 in conjunction with the first, second and third restrictor means reduces the output primary product pressure to about zero psi. A flow control valve means, such as a needle valve 62, throttles back the flow of primary product therethrough such that the primary product pressure is maintained at 2 to 6 psi upstream thereof during operation of the second compressor. In the preferred embodiment, the needle valve is adjusted such that the flow rate therethrough matches an optimum primary product output flow rate for the sieve bed assembly. That is, at different flow rates, the sieve bed assembly produces oxygen of different purities. The flow rate through the needle valve is adjusted to select the best available flow rate for the selected purity. Increasing the flow rate permitted by the needle valve tends to provide a greater volume of primary product gas but with a lower oxygen concentration; decreasing the flow rate through the needle valve tends to provide a smaller volume of primary product gas but with a higher concentration of oxygen.

With reference to FIG. 2, the control circuit F includes an on-off switch 70 connected with the nongrounded side of a 120 volt or 240 volt power supply. The first compressor 10 is connected in series with the on-off switch and power supply such that it runs continuously whenever the unit is actuated by the on-off switch 70. A cooling fan motor 72 is likewise connected in parallel with the first compressor such that it too runs continuously whenever the unit is on. A mechanical timer motor 74 is connected in parallel with the first compressor means for cyclically opening and closing a time controlled switch 76. The time controlled switch 76 is connected in series with the crossover valve 20 for cyclically moving the crossover valve between its first and second positions with a regular periodicity. The second compressor 40 is connected in series with the pressure sensing switch means 48 such that the second compressor 40 is actuated and responds to the pressure sensing switch sensing a pressure below the preselected storage pressure, e.g., below 65 psi. A time delay relay 78 is connected in parallel with the second compressor and in series with the pressure sensing switch for closing a relay means 80 a preselected duration after the pressure sensing switch is actuated, e.g., five seconds. The relay means 80 is connected in series with the compressor start up valves 42 and 44. In this manner, the compressor start up valves 42 and 44 move from a nonactuated position in which the second compressor operated under no load to the actuated position illustrated in FIG. 1 in which the second compressor draws the primary product from the pressure and flow regulator means E and pumps it to the storage tank 46.

The invention has been described with particular reference to the preferred embodiment. Various alterations and modifications will become apparent upon reading and understanding the preceding detailed description of the preferred embodiment. It is intended that the invention be construed as including all such alterations and modifications insofar as they come within the scope of the appended claims or the equivalents thereof.