(121f) Hybrid Air Separation Processes for Production of Oxygen & Nitrogen

Novel hybrid air separation processes for oxygen production that require less capital and, in some cases, lower operating costs than a conventional cryogenic distillation air separation unit (ASU) are developed. Either an unusual adsorption unit, Cycling-Zone Pressure-Swing Adsorption (CZPSA) [also known as feed purge pressure swing adsorption], or a membrane gas permeator, are used to increase the oxygen concentration with high recovery of pressurized gas to produce a richer feed for the cryogenic distillation plant.

Five cases are studied: 1. Use of the CZPSA adsorption unit before the main air compressor to increase oxygen concentrations to 23.5 % or less, 2. Use of a membrane gas permeation system before the main air compressor to increase oxygen concentrations to 23.5 % or less, 3. Use of the CZPSA adsorption unit after the main air compressor to increase oxygen concentrations to significantly higher values, 4. Use of a CZPSA unit in between the stages of the main air compressor, 5. Use of a membrane gas permeation system or a CZPSA unit before the main air compressor to increase oxygen concentrations to 23.5 % or less plus use of a CZPSA adsorption unit after the main air compressor to increase oxygen concentrations to higher values.

All cases can be applied either to new designs or for retrofitting and debottlenecking existing plants. The reason for a 23.5% limit on oxygen in cases 1, 2, and 5 is that above this concentration of oxygen more expensive materials of construction are required. Although 23.5 % is a low concentration, it represents a more than 11 % reduction in gas flow rate. This reduction in flow rate results in reduced power requirements for compression and reduced sizes of the downstream equipment.