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3 PSA dynamic model 30 Additionally, according to the model assumption, which states that mass transfer resistance at the CMS micropore-mouth dominates, the existence of a local equilibrium between the component concentration in the gas and solid phases is accepted. Since the mass transfer is the rate-limiting step rather than adsorption kinetics, the adsorption and desorption rates are considered to be much faster than the rate at which the steady-state is achieved within the adsorbent particle [78]. Therefore, the equilibrium is reached locally in a short time span, which is expressed in Eq. 3.3-5 and Fig. 3.3-4. This postulation is particularly relevant with respect to the slow-diffusing component of the gas mixture. (Eq. 3.3-5) ww*=w* kk k k sk 1/n 1/n (b p ) k 1+(b p ) k kk 3.4 Isosteric heat of adsorption Prior knowledge regarding isosteric heat of adsorption of pure components in the gas mixture is particularly important for PSA technology since it measures temperature changes within the adsorber during the adsorption (exothermic) and desorption (endothermic) steps. Therefore, the evaluation of adsorption equilibria and kinetics corresponding to local temperature levels in the system is feasible [79]. (Eq. 3.4-1) (Eq. 3.4-2) pure component (−H ) = R ln pk kg() 1/Tg = wk = wk k w* sk w*exp1− adsorption isotherms T 0 s0k k T In this work, the isosteric heat of adsorption was estimated based on the with the Clausius-Clapeyron method displayed in Eq. 3.4-1. The effect of loading as well as temperature on the adsorption enthalpy was considered since the adsorbent surface coverage θ depends on the process temperature as stated in Eq. 3.4-2. The results are presented in Fig. 3.4-1. Tab. 3.4-1 Equation and fitting parameters describing the adsorption enthalpy of oxygen and nitrogen on the CMS −H =Aw5expG+Bw4expH+Cw3expI+Dw2expJ+Ew expK+FexpL k 2.384 G × 10-1 -1.087 k T k T k T k T k T T A × 10-14 B × 10-12 C × 10-9 D × 10-6 E × 10-3 F × 10-1 O2 N2 O2 N2 -1.474 H × 10-1 8.365 4.914 I × 10-1 4.669 -8.498 J 2.793 8.454 K × 10-1 -1.921 -1.490 L × 10-1 2.548 3.906 -1.826 5.312 -7.997 6.931 -1.363 -1.084 6.320 4.032 2.323 -2.619 2.584PDF Image | Modelling and Simulation of Twin-Bed Pressure Swing Adsorption Plants
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