The combustion and NOx emission characteristics of the ultra-low volatile fuel using the novel pulverized coal self-sustained preheating combustion technology

The pyrolysis semi-char and gasification fly ash, as the by-product of coal pyrolysis and gasification technology, have difficulties in combustion application due to its ultra-low volatile content. As a potential combustion technology, the novel pulverized coal self-sustained preheating combustion technology for the fuel with the ultra-low volatile was developed. The 16 MW novel self-sustained preheating combustion pilot plant was constructed and used for the study. The operation characteristics of the novel internal fluidized bed combustor (IFBC) for pulverized coal preheating and the effects of the secondary air on combustion and nitrogen oxides (NOx) emissions were investigated. The results showed that the fuel could be preheated up to 900 °C continuously and steadily by the IFBC and then fed into the furnace to burn stably. The combustion efficiency was higher than 96% with the lowest NOx emission of 110.0 mg/m3 (@6% O2). The flame images exhibited most areas were red while the marginal area was blue. With the decrease of the secondary air ratio, the flame length and the ignition delay distance decreased, and the flame profile became blurred. Meanwhile, the NOx emissions firstly decreased and then increased with the lowest value at the secondary air ratio of 0.39. The decrease of the momentum ratio of inside secondary air to outside secondary air had a certain effect on inhibiting NOx generation until the ratio dropped to less than 0.6.