In the presence of si sink, a gas stream with high solute concentration can undergo large decreases in pressure and flow rate because of the transfer of solute. This behavior has been observed during the loading of concentrated gas adsorbers; In this paper we introduce a dynamic tray model capable of predicting gas-phase transients during the start-up of concentrated absorbers. The model accounts for gas holdup and pressure, solvent evaporation, weeping, entrainment, and downcomer holdup. The main assumptions in the model are equilibrium trays, well-mixed gas and liquid phases, and ideal gas behavior. Simulation results for the absorption of concentrated HCl gas in water and concentrated NH3 gas in water are discussed. Predictions with the model reveal severe flow and pressure transients capable of inducing excessive weeping. An alternate start-up procedure to reduce transient weeping is discussed.