CRYOGENIC METHOD OPERATING AT NORMAL PRESSURE AND BELOW FOR ENRICHING THE OXYGEN CONTENT IN AIR

摘要

Oxygen and oxygen-enrichment are nowadays produced from air generally by threernmethods: cryogenic, adsorption and membrane separation. Various methods producerndifferent purities and mass flows of oxygen. Again, the utilization of oxygen-enrichment,rnI.e. not pure oxygen, is often sufficient in many combustion applications.rnThe process introduced in this paper is a novel cryogenic method producing oxygenenrichmentrnmore energy-efficiently than the methods used till now. The mass flow of thernproduced enrichment may vary with the number of parallel basic modules applied. Due tornthe low pressures used in the introduced process (at maximum approximately 1.3 bar abs.,rnabsolute pressure), the compression work needed is smaller than e.g. in the Linde-Fr?nklrnprocess (the maximum pressure about 6.5 bar abs.), and the process approaches tornreversible. Furthermore, the main fraction in mass flow of air, I.e. the nitrogen-enrichedrnfraction, is not liquefied which saves energy compared to the common cryogenic processesrnthat liquefy this fraction. Nevertheless, the achieved low temperature of the nitrogenenrichedrnfraction is efficiently utilized in pre-cooling of the incoming process air. Since thernprocess does not produce pure oxygen, the energy required to separate the last percents ofrnoxygen from nitrogen-enriched fraction is saved. This is noticeable because of the lastrnpercents demand proportionately most separation energy.rnMoreover, the core of the process concerned consists of two nested columns that have arnheat exchange interaction with each other on their entire lengths. The adiabaticrnrectification columns used commonly nowadays only have a partial heat exchange contact,rnrespectively. Thus, the applied construction is both simple and thermodynamicallyrneconomical. Since the prevailing pressure is kept different on the various sides of the mainrnheat exchange surface, I.e. both the nested columns have different pressures, the phasernchange of the produced fraction occurs at different temperatures in the various columns.rnConsequently, the other main power source needed to maintain the process in operation isrnan air pump for compressing the low pressure product gas from the evaporation (inner)rncolumn to atmospheric pressure. The other power source is needed to feed in air into thernprocess.rnIn this paper, the novel cryogenic method operating at normal pressure and below it forrnproducing oxygen-enrichment is introduced. The theory behind the process as well as somernmodeling and experimental results are studied.