Motion and swelling of single coal particles during volatile combustion in a laminar flow reactor

Abstract

Motion and swelling behavior of single bituminous coal particles during volatile combustion are investigated in a laminar flow reactor using a joint experimental and numerical approach. Three different particle samples with mean diameters of 90, 120, and 160 µm are studied in a conventional N2/O2 atmosphere with 20 vol% O2 mole fraction. Diffuse backlight-illumination (DBI) measurements with high temporal (10 kHz) and spatial (> 19 lp/mm) resolutions, combined with detailed parameter evaluation methods, provide fundamental insights into interactions of particle with flow and flame. The acceleration behavior of different particles is assessed based on the response time following the viscosity drag law. Rotation speed is determined by temporally tracking the orientation angle and shown to strongly correlate with the particle size and the devolatilization process. Simultaneously measured slip velocity and particle diameter enable evaluating time-dependent particle Reynolds numbers Rep. The swelling behavior is temporally synchronized with the devolatilization process and reveals a strong dependency on particle diameters. To better understand experimental observations, detailed simulations are first quantitatively validated against experimental ignition delay times and then applied to predict particle temperature histories. Further, the reduction of particle heating rates with increasing diameters is numerically quantified. The maximum swelling ratio decreases from 1.22 to 1.07 as the heating rate increases from approximately 3 × 104 to 8 × 104 K/s.