Homogeneous ignition and volatile combustion of single solid fuel particles in air and oxy-fuel conditions. (1st May 2021)

• Record Type: Journal Article
• Authors: Li, Tao; Farmand, Pooria; Geschwindner, Christopher; Greifenstein, Max; Köser, Jan; Schumann, Christoph; Attili, Antonio; Pitsch, Heinz; Dreizler, Andreas; Böhm, Benjamin
• Is Part Of: Fuel. Volume 291(2021)
• Publication Date: 2021-05-01
• Subjects: Single particle combustion -- Ignition and volatile flame -- Multi-parameter laser diagnostics -- Oxy-fuel combustion -- Bituminous coal -- Combined experimental-numerical approach; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2020.120101
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: sdfdhkdjsh Highlights: Single particle combustion is investigated in a laminar flow reactor with fully-measured boundary conditions using a combined experimental-numerical approach. Multi-parameter optical diagnostics provide comprehensive data including the particle velocity, ignition delay time and volatile combustion duration. Simulations assist to interpret the experimental observations with varying particle sizes, oxygen concentrations, slip velocities, and N2 replacement by CO2 . The particle size and gas composition dominate the ignition delay time via affecting the particle heating rate. The N2 replacement with CO2 will not delay the ignition if the global gas temperature is constant. Abstract: The ignition and volatile combustion of single coal particles were investigated under laminar conditions. Relevant physico-chemical processes were analyzed under conventional and oxy-fuel atmospheres with varying O2 contents in experiments and simulations. An optically accessible laminar flow reactor with well-defined boundary conditions measured with PIV and quantitative OH-LIF was employed. Multi-parameter optical diagnostics were conducted, including OH-LIF, luminescence imaging, and backlight illumination. Simultaneously acquired experimental data allowed for the evaluation of particle size, ignition delay time, and volatile combustion duration for individual particles. A statistical analysis revealed the improved accuracy of OH-LIF compared to luminescence imaging regarding ignition detection. Simulations within an Eulerian–Lagrangian framework were introduced and validated against experiments. On this basis, particle temperatures, local gas temperatures, and fuel mass fraction were evaluated, providing insights into the devolatilization. Both experimental and numerical results indicated that increasing particle sizes significantly retarded homogeneous ignition and volatile consumption. When increasing the O2 content, a shorter ignition delay time and volatile combustion duration were observed experimentally, which was more significant for larger particles. High slip velocities accelerated convective transport resulting in an earlier ignition and faster volatile combustion. An atmosphere change from N2 to CO2 showed an earlier ignition and increased volatile combustion duration for larger particles, whereas the differences were insignificant for small particles. Simulation results suggested that the local heat transfer was improved by CO2, mainly due to the lower temperature sink close to particles and hence higher volatile release rates. As the initial ambient temperatures were similar, the introduction of CO2 favored homogeneous ignition and slowed down the volatile consumption.