Abstract: On the basis of preheating combustion technology，an internal circulating preheater for the stable combustion of
fine powdered fuel was proposed，which was aimed at the clean and efficient utilization of ultra-low volatile carbon-based
fuel.The operating characteristics of the internal circulating preheater was investigated on an internal circulating preheater
cold test rig，a 2 MW internal circulating preheating combustion pilot test rig and a 16 MW preheater testing platform
successively.Also，the characteristics of preheating，combustion and NOx emission of ultra-low volatile carbon-based fuel
were discussed.The results showed that the material balance and a stable circulation could be established in the internal
circulating preheater when fluidizing air velocity was in the range of 1.50—2.25 m/s. A stable preheating process was
realized by preheating the fuel in the internal circulating preheater steadily and continuously to 850 ℃ and above，thereby
meeting the requirement of the preheating combustion process.The high-temperature gas fuel mainly included N2，H2，CO，
CH4 and CO2. And 57.08% of nitrogen element was released in the internal circulating preheater. Proven by testing，the
combustion efficiency was higher than 97%，and NOx emission reduced to 112.7 mg/m（3@6% O2）.

Key words: internal circulating preheater, preheating combustion, ultra-low volatile carbon-based fuel, NOx emission