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purification of hydrogen, from a five component mixture in a column with two layers of adsorbent was chosen. A layer of activated carbon followed by a layer of zeolite is used for a process consisting in 9 steps with 1 or 4 beds. The considered literature studied the employment of two different mathematical models, a complete and a reduced one, and the impact of these in the results of the simulations. Loading, concentration and temperature profiles in the cyclic steady state and for some steps of the PSA process are shown in the mentioned work [39]. The mathematical model employed in the considered literature assumed that gas phase behaviour was described by the ideal gas law, no gradients in the radial direction, axial dispersed plug flow, macropore and micropore mass transfer resistances described by the LDF model, no temperature gradients inside each particle, the column wall interchanges energy with the gas phase inside the column and with the external environment, constant porosity along the bed and that the Ergun equation is valid locally. 4.3.1 Multisite Langmuir isotherm modeling The multisite Langmuir isotherm, described by equation (4.4) will then be introduced in gPROMS® library, replacing the Langmuir isotherm mentioned in chapter 3 (Equation (3.13)) with the aim of being used in PSA processes involving a multilayer adsorption bed. (4.4) 𝑞 𝑞𝑎𝑖 ( 𝑖 )=𝑎𝑖𝐾𝑖𝑝𝑖[1−∑( 𝑖 )] 𝑞𝑖,𝑚𝑎𝑥 𝑖 𝑞𝑖,𝑚𝑎𝑥 where 𝐾𝑖 = 𝐾∞ exp (− ∆𝐻). 𝑅𝑇 This equation was introduced and calculated in the same two FOR DO cycles mentioned in the multilayer and Langmuir-Freundlich models. Heat of adsorption is, once again, assumed to be a parameter for the present isotherm model and, the model was written with the same assumptions used in the other isotherm model. As it was done for the Langmuir-Freundlich model, the parameters of the isotherm were assumed to have a distribution in the components and in the axial direction due to the variation of these parameters with the temperature in the adsorption bed. The variables used to obtain these parameters were considered as arrays of the components and number of layers. During the modelling period an error occurred due to the negative values being assumed by the term raised to the parameter 𝑛𝑖, preventing gPROMS® from running the simulation with the present isotherm. In order to avoid this situation, the absolute value of the said term was used instead, with the purpose of resolving this numerical problem. Pressure Swing Adsorption for Hydrogen Purification Modelling and Simulation 34PDF Image | PRESSURE SWING ADSORPTION FOR THE PURIFICATION OF HYDROGEN
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