In the technologies of thermal energy production by burning biofuels, the air supplied for combustion is humidified by water injection, the combustion process in the furnace is regulated, and liquid reagents that reduce the concentration of toxogens are added to the flue gas flow along with water droplets. It is important to harmonize all injection cases in order to ensure the highest possible efficiency of biofuel combustion technology. The boundary conditions of the phase transformations and heat exchange of the sprayed water droplets can vary greatly, but the phase transformations of the droplets must always ensure the necessary adjustment of the flue gas parameters. In order to understand their regularities and apply them in practice, it is necessary to know the processes of droplet heat exchange and phase transformations. Experimental and numerical research was carried out in the work, and the main conclusions are presented on the basis of the obtained results. The diagram of the thermal state of the equilibrium evaporation of a water droplet summarising the results of the experimental research and the highlighted regularities of the interaction of the droplet composite transfer processes creating preconditions for the efficient regulation of water injection into the biofuel flue gas to be effectively regulated has been produced. Based on the simulation results, the diagram of the water droplet path until evaporation in the humid gas flow allows to determine the required droplet dispersity and provides the conditions for the proper organization of water injection in order to humidify the combustion air and to introduce liquid additives so that to inhibit toxogens in biofuel flue gas.