Traditional drying systems equipped with coal-fired hot blast stoves have been difficult to approve with the improvement of national environmental standards, and are gradually banned.

Since the oxygen content of the traditional flue gas direct drying system is as high as 18%, the benchmark oxygen content of the gas boiler is 3.5%, the benchmark oxygen content of the coal-fired boiler is 9%, and the discount coefficient is as high as 4.4~8.75, even if the flue gas ultra-low emission system is equipped. Exhaust emissions are also difficult to meet standards, causing many completed drying projects to stop production.

Due to the direct contact between the flue gas and the material and the high oxygen content of the system, the traditional flue gas direct drying system is prone to coal dust explosion and poor safety.