Concept of bifunctional Redox iron-chelate process for H 2S removal in pulp and paper atmospheric emissions

Abstract

Utilization of ferric chelates for the oxidation of hydrogen sulfide is beneficial from the standpoint of iron-sequestration and protection against precipitation in the alkaline environments characteristic of the Kraft mill effluents. Availability of oxygen along with hydrogen sulfide in the atmospheric emissions of pulp and paper industries is beneficial for the simultaneous Redox regeneration from ferrous to ferric chelates. By putting together these two premises, the concept of a multifunctional Redox process for the scrubbing of hydrogen-sulfide-contaminated atmospheric effluents emanating from the Kraft mills is formulated, modeled and simulated. This paper discusses from a multiphase reactor engineering perspective, the design of a countercurrent packed-bed bifunctional scrubber by setting an exhaustive modeling framework in which are solved both the oxidation of hydrogen sulfide in reactive ferric chelate solutions of ethylenediaminetetraacetic acid (EDTA chelate) and the simultaneous oxidative regeneration of ferrous chelates resulting from oxidation of hydrogen sulfide. A one-dimensional model based on the transient species balance equations in the gas and liquid phases coupled with the transient film model according to the film-penetration theory was developed for the description of the time and space evolution of the species concentrations along the scrubber. The oxidative regeneration of the ferrous chelate showed a synergistic effect resulting in increased enhancement factor for the hydrogen sulfide oxidation. Availability of plenty of oxygen in the atmospheric effluent precluded starvation of the ferric form and maintained high reaction rates of hydrogen sulphide removal along the whole reactor length.