The unsteady heat and mass transfer of sprayed water in the flue gas is modelled according to the iterative method of numerical research. The complex "droplet problem" covers the analysis of combined energy transfer in a semitransparent droplet, also combined heating and evaporation of the droplet. The surface temperature of the evaporating droplet is determined, at which the balance of energy fluxes taken to the surface and taken from the surface is reached. The thermal state mode of an evaporating droplet depends on the way of droplet heating as well. The change of thermal state and phase transformations parameters of water droplets warming in flue gas is analysed in the universal time scale. The initial evaluation of heat energy accumulated in exhaust flue gas utilization by water injection is presented. (C) 2009 Elsevier Ltd All rights reserved