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5 Validation of the mathematical model 63 measurement of temperature alteration during the production step; assuming that the propagation velocity of the temperature front is not higher than of the concentration front. Since the PSA experimental unit can be considered as a non-adiabatic system, the formation of a pure thermal wave front, as described by Pan and Basmadjian [105], will not occur. The experimental temperature profiles at investigated product purity levels are presented in Fig. 5.3.1-3. Tab. 5.3.1-4 Effect of the asymmetric pressure equalisation on the PSA performance at product purity of 10 ppm O2 (1/3) + (2/3) 12.5 + 37.5 22.40 9.83 (2/3) + (1/3) 37.5 + 12.5 25.70 8.65 * Favourable pressure equalisation strategy At low product purity the gas velocity in the packed-bed is relatively high so that the MTZ becomes elongated due to mass dispersion effects. In that case, an increase of the flow resistance in the bottom equalisation pipeline reduces the driving force for the desorption process, which results in the minor transfer of the highly oxygen-enriched gas into the bottom part of the adjacent column. Thus, the adsorption capacity in the subsequent production step is not harmfully affected. Moreover, the appropriate adjustment of the flow resistance in the top equalisation pipeline allows the straightforward transfer of the highly purified nitrogen gas into the top part of the neighbour column which supports the subsequent backflow stream. On the other hand, at high product purity, the gas velocity in the packed-bed is relatively low and the mass transfer occurs mainly in the bottom part of the adsorbent fixed-bed. In that case, the top part of the bed serves as the nitrogen safeguard bulk that ensures nearly complete oxygen rejection from the compressed air feed stream. The symmetric setting of equalisation control valves results in the highest performance, since the top part of both adsorber columns is not contacted with oxygen-enriched gas – neither in co- nor counter-current pressure equalisation stream, so the nitrogen safeguard bulk is not harmfully affected. The graphical representation of the MTZ with related favourable pressure equalisation strategies at investigated product purity levels is introduced in Fig. 5.3.1-4. These results motivate a more realistic simulation of mass transfer effects in PSA adsorbers as being state-of-the-art today. Pressure equalisation (Top) + (Bottom) Stem position [%-opening] Productivity [m3n/h N2 / m3 CMS] Air demand [m3n/h air / m3n/h N2] (0) + (1) 0 + 100 - - (1/2) + (1/2)* 25 + 25 29.64 7.78 (1) + (0) 100 + 0 - -PDF Image | Modelling and Simulation of Twin-Bed Pressure Swing Adsorption Plants
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