Specifics in the operating modes of thermosyphon air heater of steam generators №1 and №2 in TPP "Republika" at fuel switch from coal to natural gasIliya Iliev, Angel Terziev, Hristo Beloev and Christiyan IlievE3S Web Conf., 85 (2019) 01003DOI: https://doi.org/10.1051/e3sconf/20198501003