Efficient cryogenic nitrogen generators : An exergy analysis

A hybrid air separation process for oxygen production uses a membrane gas permeator with bypass to increase the oxygen concentration of the feed to 23.5% before the cryogenic distillation plant. A 23.5% limit on oxygen is required to avoid use of more expensive construction materials. By pre-concentrating the oxygen, the feed flowrate to the compressor, heat exchangers and the distillation column can be reduced by 11%, which reduces power requirements and sizes of the downstream equipment. Achieving this concentration with very low energy requirements is surprisingly difficult with commercially available membranes. New membrane materials with higher fluxes and selectivities could make the process more economical.

Hybrid Membrane-Cryogenic Distillation Air Separation Process for Oxygen Production

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...

Hybrid Air Separation Processes for Production of Oxygen and Nitrogen

In a process for the purification and separation of a synthesis gas mixture containing carbon monoxide and/or hydrogen, a synthesis gas mixture is purified in an acid gas removal unit (3) including a nitrogen stripping column to form a purified synthesis gas mixture, at least part of the purified synthesis gas mixture is sent to an adsorption unit (7) to remove methanol and/or carbon dioxide and form a further purified synthesis gas mixture, at least part of the further purified synthesis gas mixture is separated at a cryogenic temperature to form at least an N 2 /H 2 mixture or a product stream enriched in hydrogen and/or carbon monoxide, the adsorption unit is periodically regenerated using a gaseous nitrogen stream thereby producing a gaseous nitrogen stream containing methanol and/or carbon dioxide and at least part of the gaseous nitrogen stream containing methanol and/or carbon dioxide is sent to the nitrogen stripping column as a stripper gas.

Process and apparatus for the treatment of a synthesis gas

Rare (Noble) Gases

The principles of cryogenics are examined in this paper. This technology and its applications involve mainly physical rather than chemical reactions. The author notes that practically no disturbing chemical reactions occur in cryogenic processes. Among the most economically and technically important physical reactions occurring at cryogenic temperatures are the cooling and liquefaction of gases, and the distillation and franctional condensation of liquefied-gas mixtures to yield pure-component streams. Cooling and liquefaction are the basis of every cryogenic process.

H. Springmann

Papers

Cryogenics principles and applications