The ultra-low NOx emission characteristics of pulverized coal combustion after high temperature preheating

Abstract

Preheating combustion is a promising low-nitrogen combustion technology. The article mainly describes the ultra-low NOx emission characteristics during preheating combustion, including preheating characteristics, combustion characteristics, and fuel nitrogen migration and transformation characteristics. Under the condition of fluidized bed equivalence ratio of 0.63 and preheating temperature of 980 °C, the calorific value of high-temperature coal gas is about 1.75 MJ/Nm3. Compared with raw coal, preheated char is modified and upgraded with a smaller particle size, larger specific surface area, and more pore structure. The combustion temperature is about 1045 °C, and the main form of NOx (NO2 or NO) along the DFC changes with the intensity of combustion. During the preheating process, 76.1% of the fuel nitrogen is converted to N2. Only 5.9% of the fuel nitrogen is converted to NH3, and NH3 is the only precursor of NOx. The average NOx emission is 31 mg/m3 (@6% O2), and corresponding conversion ratio of fuel nitrogen to NOx is 0.85%. This experimental results will play a vital role in the development of efficient and clean coal combustion technology.