Psychrometric-like charts for the energy analysis of VOC recovery processes

Psychrometric-like charts for the energy analysis of VOC removal or recovery by means of combined adsorption and condensation were developed. These charts make use of conventional psychrometric parameters: dry-bulb temperature, specific mass content—or alternately mole fraction—, degree of saturation (relative “humidity”), enthalpy, etc., for toluene-nitrogen mixtures. In addition, they include information on the adsorption equilibrium, and particularly the adsorbed-phase enthalpy, in order to characterise the adsorbers behaviour. The graphical representations of unitary operations occurring in VOC treatment processes are presented: VOC condensation on a cool coil, adsorption or regeneration of an adsorber. This methodology is applied to a case study based on an indirectly heated and cooled adsorber and a heat pump. A proper design of this integrated process allows to use half of the heat available at the heat pump condenser, which is usually wasted.