Coal Combustion in Fuel Rich Flames: A Review of Experimental Behavior

Reaction efficiencies (11) of cokes and coals in fuel-rich flames are shown generally to obey the simple mass-balance equation: 11 = 2 (R C S) [1 + E%/lOO]; over the range -80 to -30% excess air, and for an RCS factor of O.S. This RCS factor is for carbon conversion to CO2 with no CO; it implies very fast conversion of any primary CO. The data used were obtained in different experiments using a plug-flow furnace, a jet-mix reactor, and a high-intensity furnace. The trend of reaction efficiency above -30% excess air then depended on the reactor used. With the jet-mix reactor, the reaction efficiency peaked at about the stoichiometric equivalence ratio for an enhanced VM yield (at a Q-factor of 2). Temperatures also peaked at about that equivalence ratio for both the jet-mix reactor and the high-intensity furnace. The flame mechanism appears to be combustion primarily or totally in volatiles at this fuel-rich optimum, with heterogeneous reaction providing an increasing contribution as excess air increases. With decreasing excess air, however, as discussed in the paper, this argument appears to lead to the conclusion that the extent of pyrolysis may be governed by the availability of oxygen to react with it but there are obvious difficulties with this conclusion. These results show that a reasonably clear pattern of experimental behavior still presents major difficulties in mechanistic interpretation

Pyrometer Design for 2-Color Particle Temperatures Measurements in Large Flames

Design details are given of a 2-Color (intrusive) pyrometer used to measure particle temperatures at "point" locations in "large" coal-water fuel (CWF) flames. The results using this device, and comparative measurements in the same flames obtained by suction pyrometer, have already been reported [ I ] , but not the details of the 2-C pyrometer design; these are provided in this paper. Much of the design is conventional and has been reported previously [2]. What is unique is the design of the tip of the (intrusive) probe used to pick up the radiation signal. This is designed to define a "small" volume in the flame that is the source of the signal from the radiating particles. The basis of the probe design is a 6-nun quartz rod, to pick up the radiation signal, contained in a water-cooled jacket. The view half-angle from the rod into the flame is about 3°, thus defining the bounds of the view volume perpendicular to the view direction. The view depth into the flame is limited by a water-cooled target disc that is held in position by its water-cooling tubes. This distance was generally set at about 5 cm but is adjustable. At this time the device has been used in flames iii combustion chambers of dimensions 2'x2'xIO' . In the context of these dimensions, the viewing volume is considered "point-source". Details of the signal processing are given in the earlier paper [2]; the signal analysis is based on the treatment developed by Macek and Bulik [3]. The paper includes an outline both of the signal processing and analysis procedures, and a summary of earlier pertinent results. The result of principal interest is the difference of up to 400°C between the suction pyrometer and 2-C measurements, assumed to be representative of the ambient gas and reacting particles, respectively. The other aspect of interest discussed is the potential for scale up to boiler flames

Studies in Furnace Analysis: Evaluation of Performance Characteristics of a Laboratory Furnace

I t is now well established from numerous studies of experimental and industrial furnaces that the variation of thermal input (He) with useful output (H,) for any furnace is described by the Firing Equation: where the Firing Constants, Ht , aO, and II. m, are the Idle Heat, the Intrinsic Efficiency, and the Maximum Output, respectively. The theoretical developments have broadly established the expected dependency of the Firing Constants on the equivalence ratio (Excess Air); but test of those dependencies is still limited. Using data obtained from a small laboratory furnace, this paper examines some of those dependencies, with particular attention given to Excess Air and the problem of reducing the firing data to a common stoichiometric base to be able to test the applicability of the Firing Equation. Excess Air in the experiments ranged from 10% to 55%, with the firing rate increasing appropriately. Generalization of the results obtained also shows analytically and quantitatively the low firing rate increase with Excess Air for furnaces of high Intrinsic Efficiencies, with the converse for low Intrinsic Efficiency furnaces. This result is well known qualitatively; it is not known, however, to have been reported previously as a quantitative generalization obtained analytically as presented in this paper