OCR Text |
Show required residence time. But interpreting burnout time data requires certain assumptions about the rate expressions and how the differential carbon balance is integrated. In particular, it is necessary to know how particle density and size vary with each other. When either density or size are constant, integration is greatly simplified. For the case of regime III combustion (constant density) Essenhigh (11) shows that - 2 p d z c po t, = 48 NShD' In (1 - zy , ) = K d2 . (9) b o yob D po For chemically controlled combustion of a nonporous sphere, burnout time is given by P d t -_£J£- =K d nm b . n c po. (10) cJ ob Note that equation (9) also applies to the case of a shrinking core reaction within a constant diameter sphere, if the diffusion resistance of the reacted outer layer is negligible. EXPERIMENTAL EQUIPMENT AND PROCEDURES The Tubular Reactor The tubular-flow reactor used for these experiments is illustrated in Figs. 2 and 3. Nitrogen and air mixtures were metered through rotameters into an electric preheater and then into the reactor itself. The reactor consisted of a 1 in. (2.5 cm), schedule 40 Inconel tube surrounded by an electric furnace. A quartz window at the upstream end allowed direct viewing of the samples, which were suspended in a loose ball of quartz wool (see Fig. 4). The wool, weighing between 0.02 and 0.04 g, was held in a cylindrical basket t made from either stainless steel wire screen or aluminum oxide. Except for a thin horizontal support bar across the downstream end, Comparative testing demonstrated that there were no significant difference between using the wire screen or the aluminum oxide cylinder. Most runs were made with the aluminum oxide cylinder. 9 |