Results of calculations for free-convection diffusion flames are presented for the range of external radiative fluxes encountered in room fires. The specific system studied is PMMA burning in O 2 /N 2 atmospheres. It is found that the burning rate shows a linear increase with ambient oxygen concentration at fixed external radiative flux, and shows an almost linear increase with external flux at fixed oxygen concentration. The minimum oxygen concentration required for combustion is found to decrease slowly with increasing external radiation. A criterion for estimating extinction limits based upon a parameter equivalent to a local Damkohler number is proposed.

An analytical model of a n isothennalJuc gas desu firization moving-bed reactor has been developed. The INTRODUCTIONReactors used to reduce the concentration of sulfur dioxide in flue gas through contact with solid adsorbents are generally classified as either fixed bed 151. fluidized bed [12, 131, or moving-bed reacTors [9,161. Although continuous operation can be achieved with either the fluidized bed or moving bed reactors. the reduced amount of sorbent attrition associated with Correspondence concerning this paper should he addressed to Robert Enick. E-mail: enick~enffmn~.pitt.edil. the moving bed reactors has led to increased interest in their application. Solid particles used in moving bed absorbers are typically dry, regenerable metal oxide-impregnated sorbents. such as silica or alumina. These sorbent particles are gravity fed to the reactor. where they are contacted by a cross-flowing flue gas. The sulfur dioxide in the gas stream reacts with the copper oxide on the surface of the sorbent, yielding copper sulfate. After exiting the moving bed reactor, the copper sulfate-rich sorbent particles are subsequently heated and regenerated with a reducing gas.Two geometries have been proposed for moving-bed reactors. Axicylindrical moving bed absorbers are characrerized by the radial, horizontal flow of the gases and doa-nward, vertical, annular flow of the copper oxide adsorbent particles. Gases can be collected along both the axis and the outer perimeter of the reactor, thereby permitting gas flow either toward or away from the reactor axis [Carson, 19841. Simkar reactors have been used for the desulfurization of flue gas using activated carbon [71. Reactors with rectilinear geometries are characterized by the horizontal flow of flue gases through a copper oxide bed moving in a downward. vertical direction [9,10,141. Yeh and coworkers [131 developed an analytical model of the isothermal counterflow fluidized bed reactor. ms model was later extended to the rectilinear cross-flow moving-bed reactor [161 by modeling the moving bed as a two-dimensional army of interconnected nlicroreactors. The equations governing the performance of these microreactors were derived from a differential model for gas-solid counterflow rather than the cross-flow that actually occurs in the moving bed as the downflowing sorbent removes SO2 from the gases flowing in a MATHEMATICAL MODEL OF THE ISOTHERMAL MOVING BED REACTORThe moving bed desulfurization model used in tlu study is provided in Figure 1. The flue gas enters the side of the reactor, while the sorbent particles are gravity fed into the reactor from the top. It is assumed that the horizontal gas flow is distributed over the entire side of the reactor as it passes through the screen that retains the sorbent particles. The slowly moving sorbent bed is assumed to exhibit plug flow, therefore the downward velocity of each sorbent particle is equivalent. Reaction KineticsThe desulfurization reactants include the SO, and 0, in the The SO, concentration in the flue gas ent...