Process Modeling and Optimization of a Submerged Arc Furnace for Phosphorus Production

Abstract

This article presents a process model of a phosphorus-producing, submerged arc furnace. The model successfully incorporates accurate, multifield thermodynamic, kinetic, and industrial data with computational flow dynamic calculations and thus further unifies the sciences of kinetics and equilibrium thermodynamics. The model is structurally three-dimensional and uses boundary conditions, initial values, and material specifications provided by industrial measurements, laboratory experiments, and a combination of empirical and thermodynamic data. It accounts for fully developed gas flows of gaseous product generated from within the packed bed; the energy associated with chemical reactions, heating, and melting, as well as thermal conductivity and the particle-particle radiation within the burden. The model proves the existence of a narrow, gas-solid reduction zone where the bulk of phosphorus is produced. It shows that fast reaction rates in this narrow reaction zone in combination with long residence times diminish the influence changing reaction rates have on the process. It indicates that most heat exchanged between the new pellets entering the furnace and the gaseous product produced in the reduction zone takes place in the top 0.5 m of the furnace bed. The gaseous product and flow information shows low and recirculating gaseous flow velocity areas that cause dust accumulation.

Pyrometallurgical Treatment of Apatite Concentrate with the Objective of Rare Earth Element Recovery: Part II

“…Energy consumption for a combined process to produce P 4 and CaC 2 simultaneously from apatite is theoretically superior to the current commercial results for an equivalent CaC 2 production process, indicating a net reduction of about 40% after credits for P 4 production.…”

“…1), SiO 2 is used as a flux in order to achieve operating temperatures of the order of 1500°C, and it produces a low-phosphorus slag (\ 1 wt% P) [4], which should result in a similar outcome to the silicothermic extraction experiments presented in Part I of the present article, i.e., a low final concentration of REEs. Recently published work by Karshigina et al [17] has disclosed a method using extremely concentrated nitric acid (due to the stability of the silicates) to recover REEs from high-silica discard slag produced as a by-product of the conventional carbothermic phosphorus process.…”

“…In addition, transition metals such as Fe and Mn would be expected to be present predominantly in a metal phase, as indicated by reactions (1) and (4). The metallic product would be expected to be primarily an alloy of Fe and P, i.e., ferrophosphorus.…”

“…One possible production route for both products is via carbothermic reduction of apatite [3]. The high energy consumption of the traditional Wöhler electric furnace pyrometallurgical route, e.g., reported for one furnace to be as high as 14.3 MWh/mt P 4 [4], places it at an economic disadvantage for phosphoric acid production in comparison to alternative processes such as the wet process. In the wet process, phosphoric acid is produced by the digestion of high-grade phosphate rock, e.g., apatite, using sulfuric acid, followed by filtration and subsequent vacuum concentration [5].…”

“…Extraction of phosphorus from apatite concentrate with and without iron addition has been studied, and the elemental distribution to gas, slag, and metal was estimated where possible. In addition, a process that could simultaneously produce both P 4 and CaC 2 is proposed and evaluated.…”