Figure5. Variation in (a) the Peclet number, (b) the Reynolds number, (c) maximum superficial velocity and (d) minimum fluidization velocity with time for feed flow rate of 333 kmol/h
The Peclet number quantifies the degree of dispersion introduced into the system. It is dimensionless so is more convenient than the dispersion coefficient for this purpose. A high value for the Peclet number in Figure 5a reveals that an assumption made for ignoring radial distribution of temperature and concentration is reasonable and the bed operates under plug flow conditions. Since the adsorption unit is of horizontal bed type, the Reynolds number is small, as depicted in Figure 5b. Figure 5c and d also indicates that maximum superficial velocity is kept below the minimum fluidization velocity in horizontal adsorption unit. According to Figure 5, no significant change in the Peclet number, Reynolds number and velocities is observed after entrance of adsorption bed.
Industrial plant operates in a cyclic manner and after conducting several cycles, the adsorption process approaches to a cyclic steady state. Determining the required time to reach steady state cyclic process is typically performed by iteration method. 21Figure 6 gives the simulation results in which cyclic steady state is established after three sequential running cycles in the process due to using high regeneration flow rate. Since most of feed (air) is not adsorbed on adsorbents, only few cycles is required to reach stable condition and this matter is in good agreement with literature.22Figure 6 shows that unsteady state conditions are raised due to temperature change and accumulation of energy in the bed.22 The identical component profile is observed after three cyclic processes in Figure 6a and 6b. Figure 6c shows that identical temperature is occurred in adsorption bed.