Sub-Micron Ash Aerosol Formation in Oxy-Coal Combustion at Atmospheric and Elevated Pressures

摘要

Pressurized oxy-coal combustion is regarded as a technology to minimize CO_2 emissions with potentially improved total efficiency compared with combustion at atmospheric pressure. This work intends to understand the mechanism governing sub-micron ash aerosol formation under high pressure conditions, which has been rarely studied. Oxy-coal combustion tests were conducted on a 100 kW (rated) combustor operated at atmospheric pressure (1 bar) and a 300 kW (rated) pressurized reactor at elevated pressures (8 and 15 bar). The peak temperatures in the 1-bar and 15-bar tests were closely controlled to exclude the effect of temperature difference on aerosol formation. A high-pressure sampling system was designed and used in the pressurized tests. The particle size distributions were measured using a Scanning Mobility Particle Sizer and a Serner Low Pressure Impactor. The impactor also collected ash samples for the Scanning Electron Microscope and Energy-dispersive X-ray Spectroscopy to analyze size-segregated compositions. Results show that at similar temperature but higher combustion pressure, alkali metals are more likely to exist in the condensed phase to form fine ash particles during the vaporization-condensation process. The elevated pressure also reduces the vaporization of less volatile mineral species and causes a lower concentration of sub-micron ash aerosol.