Experimental validation of a mathematical model for fixed‐bed desulfurization

Abstract

Porous particles of two commercially available ZnO sorbents differing in porosity, surface area, and pore-size distribution were reacted with H2S at 500 and 600°C in a fixed-bed reactor. Concentration breakthrough curves were determined by analyzing the effluent of the reactor using a gas chromotograph equipped with thermal conductivity and flame photometric detectors. The pore structure of samples collected from different positions in the reactor was analyzed by mercury porosimetry and gas adsorption to determine the variation of the average structural properties of the sorbent with the length of the reactor. The obtained experimental data were used to validate a fixed-bed desulfurization model, which employs detailedsubmodels for diffusion, reaction, and structure evolution in the porous sorbent particles. With the various parameters appearing in the submodels determined from independent thermogravimetric reactivity evolution experiments, the fmed-bed desulfurization model was found to be capable of providing an excellent description of the behavior of the desulfurization sorbents in a fixed-bed reactor.

Design of Entrained-Flow and Moving-, Packed-, and Fluidized-Bed Sorption Systems: Grain-Model Kinetics for Hot Coal-Gas Desulfurization with Limestone

“…In the case of large particles of calcium-based sorbents for H 2 S sorption, CaO must first be produced in situ by calcination of CaCO 3 prior to being reacted with H 2 S. Information such as pore-size distribution in the freshly formed CaO is difficult to predict with great precision, since slight variations in the calcination procedure can greatly influence the values of the specific surface area, porosity, and pore-size distribution in the final CaO product (Boynton, 1980;Borgwardt, 1989a,b;Rubiera et al, 1991;Fuertes et al, 1991Fuertes et al, , 1993. Fortunately, the shape of the breakthrough curve (in the case of a packed-bed configuration) was shown to be weakly influenced by the details built into the pellet model (Efthimiadis and Sotirchos, 1993). Under realistic operating conditions, gas flow and mass-transfer considerations are often more significant that any slight modification in the local description of the reaction kinetics.…”

Sulfidation of Mixed Metal Oxides in a Fluidized-Bed Reactor

“…The above experimental studies showed that the sulfidation temperature (at the temperature range of interest: 500-650 °C) and the composition of the reactive gas (concentration of H2 and H2O) weakly influence the desulfurization ability of the sorbents. The size of the solid reactant strongly affects the observed sulfidation rates in a differential reactor Sotirchos, 1992,1993a) and to a lesser extent in a fixed-bed reactor (Efthimiadis and Sotirchos, 1993b). The composition and the initial pore structure of the sorbent are also parameters that may change the desulfurization capacity and the H2S concentration at the exit of a reactor (Tamhankar et al, 1986; Lew et al 1989; Efthimiadis and Sotirchos, 1993c).…”