(423h) Graphical Solution for Seeking the Optimum Shape of Adsorption Isotherm in Honeycomb Rotor TSA Dehumidifiers

When the cycle time is selected properly in a well-designed dehumidifier operated with TSA, each step of adsorption/desorption can be divided into two different time zones, i.e. a transition stage appearing just after switching the step and a subsequent thermal equilibrium stage as shown in the previous paper [1]. A special humidity chart in terms of the relative humidity φ against the absolute humidity x with the constant enthalpy line h is prepared to show the air conditions in the thermal equilibrium stage. The number of theoretical plates and the humidity change Δx in each theoretical plate is sought graphically by the conventional stage-wise operation between the constant enthalpy lines of adsorption and desorption steps, based on the HETP concept. After some simplification, the bed height of each theoretical plate is given by the reciprocal of average gradient of isotherm m_n=Δq_n/Δx_n weighted with a ratio γ_n=Δx_n/Δx_n+1 of the humidity change to that in the next plate. The optimum shape of isotherm to minimize the total bed height can be sought by increasing the gradient of isotherm m_n in the next plate by a factor of square root of the ratio of humidity change γ_n. The above simplified model is proposed together with a graphical manipulation and the result is compared with the more rigorous simulation. [1] T. Hirose, ?A Simplified Analysis of Temperature Swing Adsorption In Honeycomb Rotor Dehumidifiers?, #719m, AIChE2008 CDROM Procedings, 2008