Ignition Of Single Coal Particles In O_2/N_2/CO_2 Atmospheres

摘要

Single particles of four North American coals were burned in an electrically-heated drop-tube laboratoryfurnace and their ignition delay times were assessed. A bituminous coal (Pittsburgh #8, Pennsylvania), asub-bituminous coal (River Basin, Wyodak, Wyoming), and two lignite coals (Beulah, North Dakota aswell as Titus, Texas) were included in this study. The selected particle size cut was 74 – 90 μm, tosimulate practical applications, and the furnace temperature was set at 1400 K (1127°C). Testingatmospheres in the furnace included mixtures of either oxygen and carbon dioxide, or oxygen andnitrogen. Beginning with 20% O_2 in either N_2 or CO_2, the oxygen mole fraction was increased inincrements of 10% up to a maximum of 80% O_2. Additionally, testing was performed in a 100% O_2atmosphere to determine how the particles ignite at the absence of either diluent gas. With optical accessavailable at the sides of the furnace, high-speed cinematography was conducted to capture the particletrajectory, from entry into the furnace (at the exit of the injector tube) through the onset of combustion.From these tests ignition delay times were recorded and conclusions were drawn. Results show thatreplacing N_2 with CO_2 has a major effect on prolonging the ignition delay. Increasing the oxygen molefraction in N_2 has no significant effect on the ignition delay, whereas increasing the oxygen mole fractionin CO_2 drastically reduces the ignition delay. The Beulah lignite coal experienced the lengthiest ignitiondelays in N_2, whereas the bituminous coal experienced the lengthiest ignition delay in CO_2 as well as thebiggest disparity in ignition delay with change of diluent gas. The increase in ignition delay of the coalswhen N_2 was replaced by CO_2 was larger than the corresponding increase in volumetric heat capacity(heat sink) of the resulting O_2-dilluent gas mixtures would account for.