A mathematical model of simultaneous multicomponent mass and heat transfer in a plate column has been formulated. The film theory was used to describe mass and heat transfer kinetics in both phases. Molar fluxes were calculated on the basis of an exact solution of the Maxwell-Stefan diffusion equations, and heat fluxes - using the Ackermann correction factors. A cross flow of phases through a single plate was assumed. Mass and heat balance equations were derived assuming a plug flow model of gas phase and a plug flow model of liquid phase. The proposed model enables an assessment of the effects of multicomponent mass transfer and simultaneous mass and heat transfer for distillation, condensation and absorption with a large heat effect. Results of calculation of adiabatic ammonia absorption from air to water in a sieve plate column with downcomers were presented. Results were compared with those obtained from other models described in the literature (theoretical plate, ideal mixing of gas and liquid phases, plug flow of gas phase and ideal mixing of liquid phase).