A two-temperature model of the countercurrent plug-flow reactor for two chemically interacting liquids, the dispersion (continuous) media and dispersed phase, is developed. It is shown that there is a critical velocity of the dispersion medium that delimits two types of steady-state modes. If the velocity is greater than the critical, steady-state regimes with heating the dispersed phase near its inlet are realized. In this mode, the substance dissolved in it burns out completely. If the velocity is less than the critical value, then regimes in which the maximum heating is localized near the inlet of the dispersion medium take place, with full consumption of the reactant. It is shown that the degree of localization is higher, the greater the reaction rate. A criterion for the parameters is obtained that determines the possibility of a thermal explosion during the startup of the reactor.