Union Carbide Corporation has developed an adsorptive heat recovery drying system for petrochemicals containing up to 20% water. The system uses type 3A molecular sieves as the adsorbent and operates under conditions that allow the adsorbent to retain much of the heat generated during the adsorption cycle. This heat is used in desorbing the adsorbed water during the regeneration cycle. Operating conditions are adjusted to obtain a favorable trade-off between the cost effect of the lower equilibrium water loading capacity of the molecular sieves at the higher bed temperature in the adsorption cycle and the cost effect of the lower energy and the lower volume of regeneration gas needed in the regeneration cycle. The system has been used industrially to dry 190 proof (92.4 wt%) ethanol.
On the basis of patent information, SRI estimates the plant gate cost of drying 324 million lb/yr to be nearly 60% lower than the cost of traditional azeotropic distillation (mainly because of lower steam consumption in the new process).
By: Wing Sien Fong (August 1986)
