Simulation of desulfurization in a fluidized‐bed limestone reactor

Abstract

One of the most promising techniques of sulfur dioxide removal from flue gas is sorption using a fluidized bed of limestone. Two commonly considered schemes are the passing of combustion gases through the fluidized bed of limestone or actually burning fuel, e.g., coal, within such a bed (Zielke et al., 1970). Although the latter alternative seems to be more attractive and has been under intensive investigation (Horio and Wen, 1976;Zheng et at., 1982) the former scheme is also desirable since it can be designed to operate in conjunction with existing combustors. Recently, Wormser Engineering, Inc. (Kaplan, 1982) has developed a two-stage fluidized-bed coal combustor with the bottom stage being the coal combustor and the upper stage the limestone desulfurization reactor. The design appears to provide easier temperature control and better desulfurization efficiency compared to a single-stage, fluidized-bed coal-limestone combustor.The objective of this study was to model and simulate a fluidized-bed limestone desulfurization reactor by coupling a grain model for reaction kinetics with a fluidized-bed model based on the two-phase theory. The stack gas from a combustor containing sulfur dioxide was used as the fluidizing gas. The effects of the gas and solid flow rates, bed height, limestone properties, and operating temperature on the desulfurization efficiency were investigated. MechanismThe mechanism of the desulfurization reaction involves two consecutive steps, calcination of calcium carbonate followed by reaction of calcium oxide with sulfur dioxide, i.e., and It has been observed that reaction I is usually fast a t high temperature; however, reaction I1 decreases its reaction rate rapidly as sulfation proceeds. Mathematical FormulationThe simulation model developed in this study included a grain model and a fluidized-bed model. The grain model is useful for analysis of a reaction involving a gas reactant and porous particles. It generates the conversion data with respect to reaction time within a particle. The grain model used is essentially the one proposed by Hartman and Coughlin (1976) and is not described here. Fluidized-bed modelThe fluidized-bed model proposed is based on the two-phase theory and is designed for large particle systems (d, > 1 mm). The model has the following assumptions:1. The bed is composed of two phases, the bubble and the emulsion phases.2. The volumetric flux through the bubble phase is constant throughout the bed, and the rest of the gas flows through the emulsion phase.3. The gaseous reactant disappears according to a first-order reaction Based on these assumptions, steady state material balances on the gaseous reactant A in the bubble phase and emulsion phase have the following forms:

Control of Toxic Metal Emissions from Combustors Using Sorbents: A Review

“…25,64,66,[138][139][140][141][142][143][144][145][146][147][148][149] Shadman and et al 139,[150][151][152] have demonstrated the effectiveness of sorbents (alumina, bauxite, emathlite, kaolinite, silica, limestone) for the capture of lead, cadmium, and other alkali metal vapors. Wu et al 181 extended their earlier studies to the development of a multifunctional sorbent for capture of sulfur dioxide, alkali metals, and lead.…”

Unsteady-state retention of sulfur dioxide in a fluidized bed with continual feeding of lime and limestone

“…The overall coefficient of gas exchange between the bubble and emulsion phase was estimated with the aid of which is often employed in similar systems (Ho et al, 1986; Zheng et al, 1982).…”

Applying Eulerian and Lagrangian Approaches to the Modeling of Dry Desulfurization Process in Pulverized Coal Furnaces

“…Since the middle of the 1970s, the DAP-desulfurization technique has been intensively studied, both experimentally and numerically. While many comprehensive numerical models for FBC − and various gas−solid reaction models for single particles − have been set up, comprehensive modeling of DAP on pulverized furnaces, considering most of the influence factors, are rather rarely seen in the literature . Han et al suggested a comprehensive DAP-model for pulverized-coal combustion conditions which includes SO X formation, gas−solid reaction models, the sintering effect on the sorbent, natural retention of coal ash, equilibrium of sulfation, etc.…”