OCR Text |
Show very rapidly converted to CO . 2 however, opens some questions or result is the same as that found for emed only by the oxygen available rolysis is unclear. Production and The behavior ambiguities. the char, with (with no CO); combustion of of the coal in this furnace, Superficially, the overall the extent of reaction gov-but the contribution of py-volatiles is clearly evident from the brightness of the flame behind the flame front, but no measurements in these flame types [1-5] have yet been able to confirm or deny any Q-factor enhancement of volatiles yield. The significance of enhanced VM yield, however, is largely moot in these flames as there is no time constraint in reaching the limit of combustion efficiency for the available oxygen. There is such a time constraint, however, in the jet-mix reactor and the high-intensity furnace. In the case of the jet-mix reactor, moreover, there were detailed studies of the proportioning between homogeneous and heterogeneous reaction, and of the extent of the Q-factor enhancement of VM yield (by a factor of about 1.8). The results showed that the temperature peaked at about the fuel/air stoichiometric for the enhanced (true) VM-yield, or a whole-coal equivalence ratio of about 1.5, with 100% of the combustion at that point due to volatiles alone. As the equivalence ratio was either increased Q.l decreased from that point, heterogeneous reaction played an increasing part, with a corresponding reduction in the pyrolysis combustion efficiency. This provides a clear and consistent picture, but it has to be modified by two additional sets of results. The first set is the behavior obtained with inhibitors [7] where the maximum explosibility, as measured by inert additives required, occurred at a whole coal equivalence ratio of about 2.0, corresponding to a (true) VM equivalence ratio of 1.3. This experimental result was supported by a theoretical calculation based on a thennal balance. With chemically active additives, however, the maximum explosibility appeared to be closer to the unity equivalence ratio for the volatiles, indicating that with inert additives the contribution of heterogeneous reaction on the rich side could be significant. The second set of modifying results is the behavior observed in the high-intensity furnace [Fig. 5]. At face value, excluding the coarse grind coal, these are extensions of the char and coal data obtained in the plug-flow |