OCR Text |
Show 4.3 .let-mix Reactor. The results with this reactor (Fig. 6) [6] broadly support the prior conclusions, and extend the results to very lean conditions (up to lean extinction). The fall-off of efficiency with excess air is the result of the reactor design which is intended to investigate the conditions in the backmix region only. At a given firing rate with a limited residence time that falls with increasing excess air, the reaction efficiency also falls, and likewise the tern perat ure. The temperature profile, significantly, supports the peak temperature at an equivalence ratio of 1.4 to 1.5; it also shows the fall-off to lean extinction at about 800K (500C). The peak temperatures are comparable to those obtained in the furnace with the coarse grind coal, and lower than those of the other fuels about 200 C. This difference corresponds approximately to the different levels of wall heat loss in the systems, being about 10% in the furnace, and about 20% in the jet-mix reactor. The reaction efficiency curves also support this pattern. There are two curves: one for reaction without inhibitors [6] and one for the extinction limit ) conditions using inhibitors [7]. In both cases, however, the results, first, converge to the line for RCS = 0.5; and, second, when they depart from that line they show the reaction efficiency peaking at about the same stoichiometry as for the temperatures. 5. DISCUSSION The results described present, on the one hand, some clear-cut experimental results regarding aspects of fuel-rich behavior; but OD the other hand, the mechanistic interpretation of those results raises a number of difficult questions, if not contradictions. There are clear experimental results. The first is that the reaction effi-ciency in the fuel rich region is proportional to the negative excess air over a wide range of excess air values (roughly -90% to -30%) obeying the materials balance equation (Eq. 3.2) with RCS = 0.5. The second result is that implied by |