Patent GB-190825829-A (GB)
Title: Improved Process and Apparatus for the Liquefaction of Gases more especially applicable to the Liquefaction of Air and its Separation into Commercial Oxygen and Nitrogen.
Filed: 1908-11-30
Granted: 1909-07-29
Abstract: 25,829. Marks, E. C. R., [United States Liquid Air and Oxygen Co.]. Nov. 30. Distilling liquid air and gases.-Relates to a process and apparatus for liquefying gases, more especially applicable to the liquefaction of air and its separation into commercial oxygen and nitrogen. As regards liquefaction, the process consists in compressing the gas to a high pressure, regeneratively cooling it in successive stages to eliminate moisture and impurities, expanding the cooled gas through several expansion devices in order to liquefy it, and leading the unliquefied gas in separate portions in regenerative relation with the highpressure gas at the different stages. As regards the separation of the gases, the process consists in expanding the mixed gases after compression and cooling successively to different pressures to form bodies of liquids at such pressures, and then distilling off fractions rich in the respective components by maintaining the bodies of liquid and the highpressure gas, just prior to its first expansion, in heat-interchanging relation The invention is further characterized by the form of liquefier, the arrangement of the counter-current interchangers in sections, the distribution of the expanded gas at different pressures to the sections, means whereby part of the expanded gas is caused to do external work between its passage through two interchanger sections, the construction of the interchanger sections, and the means for finally absorbing the heat of compression. The process is adapted to produce continuous liquefaction without stoppages due to the clogging of pipes by frozen carbon dioxide, lubricating-oil, and aqueous vapour, and to remove these impurities without the aid of external agents such as ammonia, ice and salt, calcium chloride, soda lime, &c. Fig. 1 shows diagrammatically a complete plant. The air is compressed in a four-stage water-jacketed compressor 3 ... 6 with inter-coolers 7 to about 4000 lb. per square inch. The heat of compression is absorbed by the atmosphere in a surface cooler 12 comprising a system of inverted U-tubes 13 of small diameter, which enter circular or elongated headers 14. The first section 18 of the counter-current interchanger reduces the temperature of the compressed air to a stage approaching the freezing point of the aqueous vapour therein, and is provided with a system of U-tubes within each jacket. The second and third sections 19, 20 reduce the temperature progressively to a stage at which all the aqueous vapour and oil are solidified, and a portion of the carbon dioxide is separated, so that they are provided with single U-tubes of larger diameter than those in section 18 in each jacket. The air now passes through a system of tubes 37, forming the innermost passage of a triple interchanger 42, to the expansion-nozzle chamber 40. This triple interchanger comprises a downward outer helix leading to an upward inner helix ending in a downward central tube in which the system of tubes are helically wound so as to provide the maximum surface for temperature interchange. Traps 10, 15, 24, 28, 32, 58, and 83 are provided wherever the direction of the compressed gas is reversed, and they serve to collect frozen aqueous vapour, oil, and carbon dioxide, which may be removed through blow-out valves 33. In the liquefier, the compressed air expands through nozzles fitted with needle valves into an intermediate chamber 41, in which a pressure of about 60 lb. per square inch is maintained, and part is allowed to expand again past a valve 49 into an outer chamber in which a pressure a little above that of the atmosphere is maintained. The unliquefied gas from the intermediate chamber passes through the intermediate passage of the triple interchanger, through interchanger section 19, then through a heater 100 to raise the temperature to about 70‹ F. before it is caused to do external work in a motor 80. The water used for cooling the compressor may be used as the heating-medium in the heater. The cold expanded air from the motor then passes successively through interchanger sections 20, 18, whence it passes to the intake of the compressor. The air from the outer chamber of the liquefier is mixed with the air from the intermediate chamber just prior to passing through the interchanger section 18. It will be seen that the unliquefied air circulates in a closed circuit through the apparatus ; the compressor is adapted to draw in automatically the air required to make up for liquefaction and leakage. The counter-current interchangers, motor, and liquefier are surrounded by heat-insulating material in the usual manner. An approximation to adiabatic expansion is thus obtained in the motor. By the provision of valves in the various pipes, the liquefier is isolated when the apparatus is first started until the interchanger sections have been cooled down sufficiently. This is effected by circulating the air in a closed circuit comprising the compressor, cooler, interchanger sections, motor 80, and the outer passages of the interchanger sections 20, 18. Owing to the different pressures maintained in the chambers of the liquefier, the contents of the intermediate and outer passages of the triple interchanger are found to be commercial nitrogen and oxygen respectively, and these products may be drawn-off at taps 97, 98.