Experimental study on particulate matter emissions in a lab-scale pressurized reactor

Pressurized oxy-combustion (POC) is a promising carbon capture and storage (CCS) technology to improve the process efficiency and economics as compared with first-generation oxy-combustion. However, compared with traditional air combustion, pollutant emissions would be significantly changed in pressurized conditions, and the sampling method has always been disputed. A novel particulate matter (PM) sampling system, consisting of a pressurized PM₁₀ cyclone, a three-stage aerosol dilution system, and a depressurization device was developed to investigate PM emissions at elevated pressure. After being depressurized, PM₁₀ size distribution in the flue gas was measured by using an Electrical Low-Pressure Impactor plus (ELPI+). The PM losses in three depressurization devices were evaluated. Results show that, compared to a needle or ball valve as a pressure regulator, the designed nozzle performed better in terms of controlling system pressure and reducing PM loss in the channel. The sampling system was then used to evaluate the effect of pressure on PM formation. At pressure, there is a greater production of PM below 30 nm, while the generation of coarse mode PM is reduced. Sulfur-based compounds in the combusting particles are prone to be evaporated into the gas phase at higher pressure, which contributes to the formation of fine mode PM, while Fe, Si, and Ca are reduced significantly. The coarse mode PM is reduced at higher pressure, which is mainly due to the weak fragmentation; as a result, more PM is captured in the PM₁₀ cyclone. Compared with O₂-N₂ conditions, the O₂-CO₂ conditions can promote the formation of the fine mode PM.