PRODUCTION OF OXYGEN BY AIR SEPARATION

摘要

Production of oxygen from air, by compressing air to relatively low pressure, e.g. to about 3 atmospheres, and passing the compressed feed air to alternate passages of a reversing heat exchanger in heat exchange relation with a nitrogen waste stream, whereby water vapor and CO2 in the feed air are frozen on the surface of the heat exchange passage. By reversing the flow streams the low pressure nitrogen waste stream now flows through the feed air passage. This causes sublimation or evaporation of the CO2 and water vapor. A portion of the feed air is withdrawn at an intermediate point in the exchanger and is further cooled in a heat exchange passage in the lower portion of a non-adiabatic fractionating device. The cooled feed air withdrawn from the heat exchanger is partly condensed by evaporating oxygen liquid product, and is fed to the partial condensing zone of the fractionating device, whereby oxygenrich liquid is condensed and withdrawn, and nitrogen is removed as overhead. The nitrogen is expanded in a turbine and is passed in countercurrent heat exchange relation to the partial condensing zone, thereby providing refrigeration to the system. The oxygen-rich liquid is reduced in pressure, e.g. to about 1 atmosphere, and is fed to the partial evaporation zone of the fractionating device whereby nitrogen-rich vapor is removed as overhead, and oxygen of about 95% purity is removed as a liquid. The waste nitrogen stream exiting the heat exchange passage of the fractionating zone is passed through one of the reversing passages of the reversing heat exchanger, the fractionation being carried out so that there is only about a 3.degree.R temperature difference between the nitrogen waste stream and the feed air at the cold end of the reversing exchanger. The oxygen product is passed through a separate passage of the reversing exchanger also in countercurrent heat exchange relation with the feed air.