Abstract: The existing capacity of 140 t/h CDQ unit of Fujian San Steel can not reach the designed capacity．The operation of CDQ chamber is difficult，and fails to meet the production requirement of coke ovens．Some problems also exist，including insufficient circulating air volume，high resistance at boiler inlet，high temperature of coke charging and floating coke．Through analysis，it is found that air ventilation area of CDQ connecting duct is not large enough and dimension of cowl is not reasonable. And this paper also provides solutions for modifying the ventilation area of the connecting duct，which helps to improve the capacity of CDQ unit and guarantees normal coke oven production．

Key words: CDQ, Connecting duct, Air ventilation area