Hybrid Air Separation Processes for Production of Oxygen and Nitrogen

Abstract

Novel hybrid air separation processes for oxygen production are developed that use an unusual adsorption unit, Cycling-Zone Pressure-Swing Adsorption (CZPSA) [also known as feed purge pressure swing adsorption], to increase the oxygen concentration of the feed to the cryogenic distillation plant. Four cases are studied: 1. CZPSA before the main air compressor increases oxygen concentrations to 23.5% or less. 2. CZPSA after the main air compressor increases oxygen concentrations to significantly higher values. 3. CZPSA in between the stages of the main air compressor increases oxygen concentration to intermediate values. 4. CZPSA before the main air compressor to increase oxygen concentrations to 23.5% or less plus CZPSA 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 and 4 is that above this concentration 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.