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5 Validation of the mathematical model 66 during regeneration step, as shown in Fig. A.6-4. Especially, the presumed desorption pressure level of 1 bar abs is not achieved while numerical simulation. It can be seen in Fig. A.6-4a that the quality of pressure profiles estimation decreases while increasing the pressure drop across the control valve. For that reason, the relative error of PSA performance approximation increases notably. Concerning the regulation of flow resistances in the equalisation pipelines, the productivity is slightly overestimated since the mathematical model underestimates the pressure at the beginning of the blow-down step, as shown in Fig. A.6-3. Therefore, the larger driving force for desorption; hence, better regeneration of the packed bed is predicted by the process simulation. Moreover, as shown in Fig. A.6-3a, the quality of pressure profiles estimation decreases while increasing the pressure drop across the control valves. As a result, the relative error of PSA performance approximation is elevated. Besides, relative errors of the air demand approximation, presented in Tab. 5.3.1-5, originate in inaccuracies of the productivity prediction. Tab. 5.3.1-6 Cv values applied for investigating the asymmetric pressure equalisation (1/3) + (2/3) 12.5 + 37.5 1.25 × 10-5 2.85 × 10-5 (2/3) + (1/3) 37.5 + 12.5 2.85 × 10-5 1.25 × 10-5 Additionally, the effect of asymmetric settings of equalisation valves on the PSA performance was studied numerically, whilst other control valves have remained in their individual optimum position of the stem. Applied flow coefficients Cv are presented in Tab. 5.3.1-6. The results are shown in Tab. 5.3.1-7–8 and Fig. 5.3.1-6–7. Tab. 5.3.1-7 PSA performance at asymmetric pressure equalisation at reference process conditions at product purity level of 1000 ppm O2 No. 1 2 3 4 5 Pressure equalisation (Top) + (Bottom) Stem position [%-opening] Cv [kmol/s/bar] (Top) Cv [kmol/s/bar] (Bottom) (0) + (1) 0 + 100 - - (1/2) + (2/2) 25 + 25 2.50 × 10-5 2.50 × 10-5 (1) + (0) 100 + 0 - - Pressure equalisation (Top) + (Bottom) Productivity [m3n/h N2 / m3 CMS] Air demand [m3n/h air / m3n/h N2] EXP SIM Φ [%] EXP SIM Φ [%] (0)+(1) - - - - - - (1/2) + (2/2) 97.35 97.60 -0.26 3.18 3.147 1.04 (1) + (0) 84.25 51.40 38.99 3.52 4.766 -35.40 (1/3) + (2/3) 84.50 89.40 -5.80 3.47 3.386 2.42 (2/3) + (1/3) 99.15 98.70 0.45 3.13 3.139 -0.29 The model predicts the influence of asymmetric settings of equalisation valves sufficiently, regardless of the applied strategy and purity level. The only exception remains the simulation of the PSA process with a fully-opened top equalisation valve and a fully-closed bottom equalisation valve at product purity of 1000 ppm O2. The productivity is significantly underestimated, most probably due to the overestimation of gas interstitial velocity during thePDF Image | Modelling and Simulation of Twin-Bed Pressure Swing Adsorption Plants
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