Manuel Perez-Tello

Compositional Fragmentation Model for the Oxidation of Sulfide Particles in a Flash Reactor

A mathematical model to predict the size distribution and chemical composition of a cloud of sulfide particles during high-temperature oxidation in a flash reactor is presented. The model incorporates the expansion and further fragmentation of the reacting particles along their trajectories throughout the reaction chamber. A relevant feature of the present formulation is its flexibility to treat a variety of flash reacting systems, such as the flash smelting and flash converting processes. This is accomplished by computing the chemical composition of individual particles and the size distribution and overall composition of the particle cloud in separate modules, which are coupled through a database of particle properties previously stored on disk. The flash converting of solid copper mattes is considered as an example. The model predictions showed good agreement with the experimental data collected in a large laboratory reactor in terms of particle size distribution and sulfur remaining in the population of particles. The cumulative contribution and distribution coefficients are introduced to quantify the relationship between specific particle sizes in the feed and those in the reacted products upon oxidation, the latter of which has practical implications on the amount and chemical composition of dust particles produced during the industrial operation.

Size distribution analysis for copper matte particles oxidized under flash-converting conditions

Mathematical correlations were developed to represent the size distributions of high-grade (72%) copper matte particles oxidizedunder flash-converting conditions in a large laboratory furnace. The correlation parameters for the oxidized particles were expressed as functions of the operating conditions in the furnace, namely, the mean size of the feed material and the oxygen-to-matte ratio. The statistical correlation parameter r2 obtained with the mathematical expressions averaged 0.95 for the feed particles and 0.99 for the oxidizedparticles. The mathematical correlations were used to compute the amount of dust generated during the experimental runs. Good agreement between the correlated values and the experimental data was obtained. The potential application of the mathematical correlations for an industrial operation is discussed.

The Role of Expansion and Fragmentation Phenomena on the Generation and Chemical Composition of Dust Particles in a Flash Converting Reactor

A compositional fragmentation model was used to clarify the effect of expansion and fragmentation phenomena on the generation and chemical composition of dust particles in a flash converting reactor. A fragmentation index is introduced to represent the fraction of particles undergoing fragmentation, as opposed to expansion, within the particle population. Under typical operating conditions, the local dust content and the net amount of dust generated compared with the dust content in the feed first decreased and then increased along the reactor length, whereas the amount of particles undergoing fragmentation (fragmentation index) increased steadily. Dust generation was found to be the result of two competing phenomena, i.e., the expansion of dust particles in the feed and the production of dust from fragmentation of large particles. At short distance from the burner tip, the dust mostly consists of particles in the feed undergoing oxidation and expansion, whereas farther down the reactor it mostly consists of fragments of partially reacted particles. Based on the computer simulations under a variety of experimental conditions, a map of dust generation against fragmentation index was developed. For most practical purposes, dust generation may be approximated by the change in the mass fraction of dust in the population. At the reactor exit, the composition of the dust is approximately the same as the entire particle population.

The effect of bulk concentration gradient on fluid-solid reaction rate

Abstract Considerable attention has been paid to the development of mathematical models to describe fluid–solid reaction systems as they play a significant role in many chemical, metallurgical, and other engineering areas. The present work is aimed at examining one of the assumptions generally made in the mathematical modeling of fluid–solid reaction systems; namely, that the bulk concentration of the fluid reactant is uniform around the solid surface. This is a reasonable assumption under well-mixed conditions of the fluid phase. However, under certain conditions, concentration gradients in the axial direction in the fluid near the surface may be present; a packed bed is an example of such a case. It is of interest to investigate how large the concentration gradient should be before the assumption of a uniform bulk concentration around a pellet to cause a significant error. The effect of a fluid concentration gradient has been studied for a catalytic reaction on the external surface of a nonporous sphere. Petersen et al. (1964) found that external concentration gradients do not significantly affect the overall reaction rate except for the case of a second-order reaction when the reactant concentration drops from its maximum value to zero over the distance of a particle diameter, which is a rather unlikely situation in practice. Similar results were obtained by Acrivos and Chambre (1957), who recommended the use of this approximation with caution when a series of consecutive reactions takes place. In many fluid–solid reactions, the reaction progresses towards the interior of the pellet as the solid reactant near the external surface is consumed, leaving behind either a porous solid product or inert solid matrix. Although it is generally believed that a bulk concentration gradient does not significantly affect the behavior of most noncatalytic fluid–solid reactions of industrial relevance, no formal verification of this statement has yet been provided in the literature. In this work, the validity of this hypothesis is tested for a simple fluid–solid reaction configuration.