This air heaters specially designed for spray drying plants in order to ensure the best possible economy and reliability. The HAG has high overall thermal efficiency of 86 ± 1% on gross calorific value (GCV) of fuel oil and 93 ± 1% on net califoric value (NCV) of fuel oil/stack temperature of less than 200^oC and compared to electrical heating saves 80% energy. It consists of concentric cylinders through which the air and combustion gas circulate without getting in touch with each other, High thermal efficiency, high corrosion resistance, and minimal air pressure drop are some of the main advantages found through many years of operation within a great number of industries.