| OCR Text |
Show initial diameters were used: 106-125 and 75-106 /l-m. In situ measurements of particle diameter, temperature, and velocity were obtained at approximate residence times of 72, 95, and 117 ms. The coal heatup and devolatilization times extended to approximately 40 ms for the large particles and approximately 30 ms for the smaller particles, as determined by observing the luminescence of the volatile clouds around the particles. The particles were sampled at the same three residence times in the flame where the in situ measurements were taken. Solid samples were also collected at a particle residence time of 47 ms. Luminosity from coal volatiles combustion prevented meaningful in situ measurements at this earlier residence time. The samples were extracted with a helium-quench probe and deposited on a filter with l/l-m size openings. These samples were then analyzed for their elemental composition by inductively coupled plasma atomic emission (ICP-AE) spectroscopy. Elemental analyses included Fe, Si, AI, Na, Ca, K, and Ti. Additional analyses for H20, C, H, N, S, and ° were completed. 3 Determination of Overall Mass Loss Several of the elemental analyses discussed above can be used to estimate the overall particle mass loss, which will be used to determine the evolution of the mineral constituents. The analysis for overall mass loss is performed by selecting as a tracer an element which is not released from the coal/char particle during the combustion process. Additionally, the mass of coal fed into the reactor and the mass of char collected provide a measure of the overall fractional mass loss. The mass loss is determined from the concentration of a tracer as, m(t) Xi,o mo Xi(t) (1) where m(t)/mo is the fractional total mass lost at residence time t, and Xi,o/Xi(t) is the ratio of the initial mass percent of the tracer (element) i in the sample to its value at time t. There are several elements which are candidates for performing the calculation indicated above. Titanium can be recommended as a good choice based on its low evolution rate at high temperatures and presence in measurable quantities in most coals [Mims et al., 1979; Harvey and Ruch, 1986]. The natural abundance of titanium, however, is typically 1 percent or less of the total ash. While this concentration is above the detection limits of modern ICP / AE analyses, the measurement of a small fraction of a large quantity is subject to error. Elements which are bound in 3 |
