| OCR Text |
Show to determine the particle temperature change in terms of the rate at which energy is transferred to the particle by conduction and radiation, and the rate at which it is generated or consumed due to chemical reactions or phase changes. The overall rate of oxidation of the particle is determined by accounting for the various resistances resulting from the gas boundary layer, reaction kinetics, and, if a melt is present, the liquid boundary layer. The reaction rate is based on the external surface of the particle, and is obtained by combining the intrinsic reaction and pore diffusion steps, and by assuming it to be first order in oxygen concentration. A detailed description of the model equations and solution method is presented elsewhere. 10 EXPERIMENTAL All combustion and deposition experiments were conducted in a resistanceheated entrained flow reactor, operated under well characterized laminar flow conditions. Schematics of the reactor and the collection probes are shown in Figure 2. Samples of size-graded pyrite were entrained in an air stream and injected axially into the isothermal furnace via a water-cooled injector at rates of 0.1 - 0.5 gm/minute. Primary gas, consisting of 3 percent oxygen and. 97 percent nitrogen, was injected separately through the top of the reactor. Gas temperature was held constant throughout the course of the experiments at around 1500 K. Particle residence time within the 1.3 m isothermal section was varied from about 0.3 to 1.0 seconds by varying the location of the injection probe. The particles were collected at the bottom of the reactor via one of the following techniques: 1. isokinetic sampling, via a water-cooled nitrogen-quenched probe. At the exit of this probe, all particles passed through a seven stage Pollution 6 |
