Abstract:
As a novel low-carbon combustion strategy, ammonia mixing with pulverized coal combustion has gradually attracted widespread attention. However, the addition of ammonia alters the combustion process of pulverized coal, leading to changes in the generation characteristics of coal-fired particulate matter. This paper conducts an experimental study on the impact of ammonia mixing ratio and combustion temperature on the generation characteristics of particulate matter based on a flat flame burner. Particulate matter at 230 mm above the burner was collected using an ELPI(Electrical Low Pressure Impactor). Analysis of the mass particle size distribution, microscopic morphology, and elemental distribution of the particulate matter was conducted using detection methods such as SEM-EDS(Scanning Electron Microscope-Energy Dispersive Spectrometer). It was found that PM
10 under operating conditions exhibited a bimodal distribution, with significant differences in particulate matter of different modes due to different generation mechanisms. Fine-mode particulate matter had a particle size range of 0.03-0.3 μm, with a particle concentration ranging from 0.01-0.2 mg/m
3. Coarse-mode particulate matter has a particle size range of 0.3-10 μm, with a particle concentration ranging from 0.2-18 mg/m
3. Fine-mode particulate matter was primarily composed of floccules formed by the cooling of inorganics in the flue gas, while coarse-mode particulate matter was primarily formed by the coke fragmentation of coal particles after the co-combustion of ammonia and coal, taking the shape of spherical and quasi-spherical particles. Fine-mode particulate matter was rich in Ca and Na, with Ca content greater than Na, while coarse-mode particulate matter was primarily composed of Si and Al, with Si content greater than Al. Both reducing the combustion temperature and increasing the ammonia mixing ratio result in a decrease in particulate matter concentration. This was because reducing the combustion temperature slows down the heating rate of pulverized coal particles during combustion, slowed down the release rate of volatiles, led to incomplete combustion of pulverized coal particles, and reduced the thermal stress and internal pressure of coal particles. As the ammonia mixing ratio increased, the water vapor produced by ammonia combustion reacts with high-temperature coke particles, reducing the rate of change in the surface temperature of coke particles. Both factors reduce the probability of coke fragmentation, ultimately reducing the generation of PM
10.