Showing papers by "Alberto Abad published in 2004"

Selection of Oxygen Carriers for Chemical-Looping Combustion

Abstract: Chemical-looping combustion (CLC) has been suggested as an energetically efficient method for capture of carbon dioxide from the combustion of fuel gas. This technique involves the use of an oxygen carrier that transfers oxygen from the air to the fuel, preventing direct contact between them. The oxygen carrier is composed of a metal oxide as an oxygen source, and an inert as a binder for increasing the mechanical strength of the carrier. In this work, 240 samples composed of 40−80% of Cu, Fe, Mn, or Ni oxides on Al2O3, sepiolite, SiO2, TiO2, or ZrO2 were prepared by mechanical mixing as cylindrical extrudates. The samples were sintered at four temperatures between 950 and 1300 °C. The effects of the chemical nature and composition of the carrier and the sintering temperature were investigated by reactivity tests in a thermogravimetric analyzer using CH4 as fuel, and the mechanical strength of the solids. On the basis of these properties, the most promising carriers to be used in a CLC system were selecte...

Simultaneous Calcination and Sulfidation of Calcium-Based Sorbents

Abstract: This work analyzes the simultaneous calcination and sulfidation of a dolomite and a limestone during the H2S retention under calcining conditions. The experiments have been carried out in a thermog...

Effect of Pressure on the Sulfidation of Calcined Calcium-Based Sorbents

Abstract: The sulfidation process for two calcined limestones and a fully calcined dolomite was analyzed under pressurized conditions (up to 1.0 MPa), at temperatures of 723−1173 K, and with sorbent particle sizes of 0.25−2.0 mm. The sulfidation experiments were performed in a pressurized thermogravimetric analyzer and in a pressurized differential reactor. The effects of total pressure, temperature, sorbent particle size, and H2S concentration were analyzed. The sulfidation rate of the sorbents increased with total pressure when the volume fraction of H2S was constant. However, the sulfidation rate decreased with total pressure when the partial pressure of H2S was constant. A reaction order on H2S of 1 was obtained at the different total pressures that were analyzed. In addition, the rate of H2S retention decreased as the sorbent particle size increased. The changing grain-size model, with the effective gas diffusivity in the pores and the effective diffusivity in the product layer varying with the total pressure,...

Hot Coal-Gas Desulfurization with Calcium-Based Sorbents in a Pressurized Moving-Bed Reactor

Abstract: The performance of a pressurized moving bed on hot coal-gas desulfurization was analyzed for the countercurrent and cocurrent configurations. The behavior of several calcium-based sorbents, two limestones, and a dolomite was determined at temperatures in the range of 1073−1273 K and a pressure of 1 MPa. The limestones were used only under calcining conditions, whereas the dolomite was used under both calcining and noncalcining conditions. The desulfurization level and sorbent conversion, as well as the longitudinal H2S concentration profiles in the transference zone, were determined as a function of the main design and operating variables, including the Ca/S molar ratio, the bed height, the type of flow configuration (countercurrent or cocurrent), the temperature, the H2S concentration, and the particle size. The length of the transference zone, and then the reactor length necessary for full desulfurization, was highly dependent on the particle size and the solids velocity. In both countercurrent and cocu...

Direct Sulfidation of Half-Calcined Dolomite under Pressurized Conditions

Abstract: There are pressurized gasification systems in which the desulfurization process is carried out with Ca-based sorbents at noncalcining conditions. At these conditions, the H2S reacts directly with CaCO3. The direct sulfidation reaction of a half-calcined dolomite was analyzed under atmospheric and pressurized conditions (up to 1.0 MPa), temperatures between 923 and 1123 K, and with sorbent particle sizes between 0.4 and 2.0 mm. The half-calcined dolomite reacts quickly up to high conversions (>85%), and it is an effective sorbent at noncalcining conditions. The sulfidation experiments were performed in an atmospheric thermogravimetric analyzer and a pressurized differential reactor. The effects of the reaction pressure and temperature, sorbent particle size, and H2S concentration were analyzed. The changing grain size model was used to predict the experimental results and to determine the kinetic parameters of the direct sulfidation reaction. The resistances to the global reaction considered in the model w...