Ignition characteristics of isolated coal particles under pressurized oxy-fuel combustion conditions

Abstract

Pressurized oxy-fuel combustion (POC), an advanced iteration of oxy-fuel combustion, is regarded as one of the most promising technologies for CO₂ capture. In this study, the ignition characteristics of Shenhua bituminous and Jincheng anthracite under POC conditions ranging from 0.1 to 0.9 MPa were investigated using an optically-accessible pressurized flat-flame reactor (OPFFR). The ignition process was particle-resolved optical diagnosed by an in-house developed particle-tracking image pyrometer (PTIP) system. The results indicate that multiple ignition modes can coexist under the same conditions. The ratio of heterogeneous ignition is approximately 0.8 at atmospheric pressure, and this ratio decreases with increasing pressure, reaching a minimum of 0.3 at 0.9 MPa with a 30 % O₂/CO₂ atmosphere. As pressure increases, the delay for homogeneous ignition lengthens, while the change in heterogeneous ignition delay remains relatively small. Under atmospheric-pressure O₂/N₂ conditions, the homogeneous ignition delay time for bituminous coal is about 7–10 ms, whereas under the same oxygen concentration and POC conditions, it is 12–15 ms. A heterogeneous ignition model based on Semenov thermal ignition theory was developed to predict the ignition delay times under POC conditions.