| OCR Text |
Show An application in which FLASHCHAIN is used to simulate a drop tube pyrolysis test is illustrated in Figs. Sa-c. The particle thermal history in Fig. Sa is based on injection of 90 Jlm particles of an hv A bituminous coal into N2 at 1800 K within a flowtube maintained at 1000 K. The simulation accounts for moisture evaporation, convection mediated by blowing of volatiles, and radiation to the furnace walls, and implements ' temperature-dependent thennal properties of the gases plus a specific heat for coal that depends on both temperature and composition. The nominal particle heating rate is predicted to be about Sx 104 K1s, and is surprisingly unifonn throughout the test. The factor that prevents the temperature from reaching a saturation plateau after ISms is the coal's specific heat, which passes through a maximum at this point, in conjunction with the diminishing density of the particles as they lose their volatile matter. As both specific heat and density diminish, the particle heating rate increases, counteracting the tendency for the temperature to approach an asymptote. Of course, for longer times the particles would achieve a quasi-steady temperature, although devolatilization is complete after 2S ms for this case. 1750 1500 ~ .Q...) -::l 1250 .a..s. Q) a. .QE.-) 1000 Q) (3 of: 750 as a.. 500 o 5 10 15 20 25 30 Time, ms Fig. Sa. Simulated thennal history of a 90 J..Ull hvA bituminous coal particle injected into N2 at 1800 K within a drop tube furnace at 1000 K. 7 |
